| Message ID | 20220421031738.3168157-1-pcc@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: make minimum slab alignment a runtime property | expand |
On Wed, Apr 20, 2022 at 08:17:38PM -0700, Peter Collingbourne wrote: > When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum > slab alignment to 16. This happens even if MTE is not supported in > hardware or disabled via kasan=off, which creates an unnecessary > memory overhead in those cases. Eliminate this overhead by making > the minimum slab alignment a runtime property and only aligning to > 16 if KASAN is enabled at runtime. > > On a DragonBoard 845c (non-MTE hardware) with a kernel built with > CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android > boot I see the following Slab measurements in /proc/meminfo (median > of 3 reboots): > > Before: 169020 kB > After: 167304 kB > > Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead > Signed-off-by: Peter Collingbourne <pcc@google.com> > --- > arch/arc/include/asm/cache.h | 4 ++-- > arch/arm/include/asm/cache.h | 2 +- > arch/arm64/include/asm/cache.h | 19 +++++++++++++------ > arch/microblaze/include/asm/page.h | 2 +- > arch/riscv/include/asm/cache.h | 2 +- > arch/sparc/include/asm/cache.h | 2 +- > arch/xtensa/include/asm/processor.h | 2 +- > fs/binfmt_flat.c | 9 ++++++--- > include/crypto/hash.h | 2 +- > include/linux/slab.h | 22 +++++++++++++++++----- > mm/slab.c | 7 +++---- > mm/slab_common.c | 3 +-- > mm/slob.c | 6 +++--- > 13 files changed, 51 insertions(+), 31 deletions(-) [+Cc slab people, Catalin and affected subsystems' folks] just FYI, There is similar discussion about kmalloc caches' alignment. https://lore.kernel.org/linux-mm/20220405135758.774016-1-catalin.marinas@arm.com/ It seems this is another demand for runtime resolution of slab alignment, But slightly different from kmalloc as there is no requirement for DMA alignment. > > diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h > index f0f1fc5d62b6..b6a7763fd5d6 100644 > --- a/arch/arc/include/asm/cache.h > +++ b/arch/arc/include/asm/cache.h > @@ -55,11 +55,11 @@ > * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses > * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit > * alignment for any atomic64_t embedded in buffer. > - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed > + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed > * value of 4 (and not 8) in ARC ABI. > */ > #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC) > -#define ARCH_SLAB_MINALIGN 8 > +#define ARCH_SLAB_MIN_MINALIGN 8 > #endif > Why isn't it just ARCH_SLAB_MINALIGN? > extern int ioc_enable; > diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h > index e3ea34558ada..3e1018bb9805 100644 > --- a/arch/arm/include/asm/cache.h > +++ b/arch/arm/include/asm/cache.h > @@ -21,7 +21,7 @@ > * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers. > */ > #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) > -#define ARCH_SLAB_MINALIGN 8 > +#define ARCH_SLAB_MIN_MINALIGN 8 > #endif > > #define __read_mostly __section(".data..read_mostly") > diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h > index a074459f8f2f..38f171591c3f 100644 > --- a/arch/arm64/include/asm/cache.h > +++ b/arch/arm64/include/asm/cache.h > @@ -6,6 +6,7 @@ > #define __ASM_CACHE_H > > #include <asm/cputype.h> > +#include <asm/mte-def.h> > > #define CTR_L1IP_SHIFT 14 > #define CTR_L1IP_MASK 3 > @@ -49,15 +50,21 @@ > */ > #define ARCH_DMA_MINALIGN (128) > > -#ifdef CONFIG_KASAN_SW_TAGS > -#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > -#elif defined(CONFIG_KASAN_HW_TAGS) > -#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE > -#endif > - > #ifndef __ASSEMBLY__ > > #include <linux/bitops.h> > +#include <linux/kasan-enabled.h> > + > +#ifdef CONFIG_KASAN_SW_TAGS > +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > +#elif defined(CONFIG_KASAN_HW_TAGS) > +static inline size_t arch_slab_minalign(void) > +{ > + return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE : > + __alignof__(unsigned long long); > +} > +#define arch_slab_minalign() arch_slab_minalign() > +#endif > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. What about writing a new helper something like kasan_is_disabled() instead? > #define ICACHEF_ALIASING 0 > #define ICACHEF_VPIPT 1 > diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h > index 4b8b2fa78fc5..ccdbc1da3c3e 100644 > --- a/arch/microblaze/include/asm/page.h > +++ b/arch/microblaze/include/asm/page.h > @@ -33,7 +33,7 @@ > /* MS be sure that SLAB allocates aligned objects */ > #define ARCH_DMA_MINALIGN L1_CACHE_BYTES > > -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES > +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES > > /* > * PAGE_OFFSET -- the first address of the first page of memory. With MMU > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h > index 9b58b104559e..7beb3b5d27c7 100644 > --- a/arch/riscv/include/asm/cache.h > +++ b/arch/riscv/include/asm/cache.h > @@ -16,7 +16,7 @@ > * the flat loader aligns it accordingly. > */ > #ifndef CONFIG_MMU > -#define ARCH_SLAB_MINALIGN 16 > +#define ARCH_SLAB_MIN_MINALIGN 16 > #endif > > #endif /* _ASM_RISCV_CACHE_H */ > diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h > index e62fd0e72606..9d8cb4687b7e 100644 > --- a/arch/sparc/include/asm/cache.h > +++ b/arch/sparc/include/asm/cache.h > @@ -8,7 +8,7 @@ > #ifndef _SPARC_CACHE_H > #define _SPARC_CACHE_H > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > > #define L1_CACHE_SHIFT 5 > #define L1_CACHE_BYTES 32 > diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h > index 4489a27d527a..e3ea278e3fcf 100644 > --- a/arch/xtensa/include/asm/processor.h > +++ b/arch/xtensa/include/asm/processor.h > @@ -18,7 +18,7 @@ > #include <asm/types.h> > #include <asm/regs.h> > > -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT > +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT > > /* > * User space process size: 1 GB. > diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c > index 626898150011..8ff1bf7d1e87 100644 > --- a/fs/binfmt_flat.c > +++ b/fs/binfmt_flat.c > @@ -64,7 +64,10 @@ > * Here we can be a bit looser than the data sections since this > * needs to only meet arch ABI requirements. > */ > -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN) > +static size_t flat_stack_align(void) > +{ > + return max_t(unsigned long, sizeof(void *), arch_slab_minalign()); > +} > > #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */ > #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */ > @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start > sp -= 2; /* argvp + envp */ > sp -= 1; /* &argc */ > > - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN; > + current->mm->start_stack = (unsigned long)sp & -flat_stack_align(); > sp = (unsigned long __user *)current->mm->start_stack; > > if (put_user(bprm->argc, sp++)) > @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm) > #endif > stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */ > stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */ > - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN); > + stack_len = ALIGN(stack_len, flat_stack_align()); > > res = load_flat_file(bprm, &libinfo, 0, &stack_len); > if (res < 0) > diff --git a/include/crypto/hash.h b/include/crypto/hash.h > index f140e4643949..442c290f458c 100644 > --- a/include/crypto/hash.h > +++ b/include/crypto/hash.h > @@ -149,7 +149,7 @@ struct ahash_alg { > > struct shash_desc { > struct crypto_shash *tfm; > - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN); > + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN); > }; > > #define HASH_MAX_DIGESTSIZE 64 > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 373b3ef99f4e..80e517593372 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object); > #endif > > /* > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment. > * Intended for arches that get misalignment faults even for 64 bit integer > * aligned buffers. > */ > -#ifndef ARCH_SLAB_MINALIGN > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > +#ifndef ARCH_SLAB_MIN_MINALIGN > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > +#endif > + > +/* > + * Arches can define this function if they want to decide the minimum slab > + * alignment at runtime. The value returned by the function must be > + * >= ARCH_SLAB_MIN_MINALIGN. > + */ Not only the value should be bigger than or equal to ARCH_SLAB_MIN_MINALIGN, it should be compatible with ARCH_SLAB_MIN_MINALIGN. > +#ifndef arch_slab_minalign > +static inline size_t arch_slab_minalign(void) > +{ > + return ARCH_SLAB_MIN_MINALIGN; > +} > #endif > > /* > * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned > - * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN > + * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN > * aligned pointers. > */ > #define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN) > -#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MINALIGN) > +#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MIN_MINALIGN) > #define __assume_page_alignment __assume_aligned(PAGE_SIZE) > > /* > diff --git a/mm/slab.c b/mm/slab.c > index 0edb474edef1..97b756976c8b 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -3009,10 +3009,9 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep, > objp += obj_offset(cachep); > if (cachep->ctor && cachep->flags & SLAB_POISON) > cachep->ctor(objp); > - if (ARCH_SLAB_MINALIGN && > - ((unsigned long)objp & (ARCH_SLAB_MINALIGN-1))) { > - pr_err("0x%px: not aligned to ARCH_SLAB_MINALIGN=%d\n", > - objp, (int)ARCH_SLAB_MINALIGN); > + if ((unsigned long)objp & (arch_slab_minalign() - 1)) { > + pr_err("0x%px: not aligned to arch_slab_minalign()=%d\n", objp, > + (int)arch_slab_minalign()); > } > return objp; > } > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 2b3206a2c3b5..33cc49810a54 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -154,8 +154,7 @@ static unsigned int calculate_alignment(slab_flags_t flags, > align = max(align, ralign); > } > > - if (align < ARCH_SLAB_MINALIGN) > - align = ARCH_SLAB_MINALIGN; > + align = max_t(size_t, align, arch_slab_minalign()); > > return ALIGN(align, sizeof(void *)); > } > diff --git a/mm/slob.c b/mm/slob.c > index 40ea6e2d4ccd..3bd2669bd690 100644 > --- a/mm/slob.c > +++ b/mm/slob.c > @@ -478,7 +478,7 @@ static __always_inline void * > __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller) > { > unsigned int *m; > - int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); > + int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign()); > void *ret; > > gfp &= gfp_allowed_mask; > @@ -555,7 +555,7 @@ void kfree(const void *block) > > sp = virt_to_folio(block); > if (folio_test_slab(sp)) { > - int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); > + int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign()); > unsigned int *m = (unsigned int *)(block - align); > slob_free(m, *m + align); > } else { > @@ -584,7 +584,7 @@ size_t __ksize(const void *block) > if (unlikely(!folio_test_slab(folio))) > return folio_size(folio); > > - align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); > + align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign()); > m = (unsigned int *)(block - align); > return SLOB_UNITS(*m) * SLOB_UNIT; > } > -- > 2.36.0.rc0.470.gd361397f0d-goog > >
On Thu, Apr 21, 2022 at 5:30 AM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote: > > On Wed, Apr 20, 2022 at 08:17:38PM -0700, Peter Collingbourne wrote: > > When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum > > slab alignment to 16. This happens even if MTE is not supported in > > hardware or disabled via kasan=off, which creates an unnecessary > > memory overhead in those cases. Eliminate this overhead by making > > the minimum slab alignment a runtime property and only aligning to > > 16 if KASAN is enabled at runtime. > > > > On a DragonBoard 845c (non-MTE hardware) with a kernel built with > > CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android > > boot I see the following Slab measurements in /proc/meminfo (median > > of 3 reboots): > > > > Before: 169020 kB > > After: 167304 kB > > > > Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead > > Signed-off-by: Peter Collingbourne <pcc@google.com> > > --- > > arch/arc/include/asm/cache.h | 4 ++-- > > arch/arm/include/asm/cache.h | 2 +- > > arch/arm64/include/asm/cache.h | 19 +++++++++++++------ > > arch/microblaze/include/asm/page.h | 2 +- > > arch/riscv/include/asm/cache.h | 2 +- > > arch/sparc/include/asm/cache.h | 2 +- > > arch/xtensa/include/asm/processor.h | 2 +- > > fs/binfmt_flat.c | 9 ++++++--- > > include/crypto/hash.h | 2 +- > > include/linux/slab.h | 22 +++++++++++++++++----- > > mm/slab.c | 7 +++---- > > mm/slab_common.c | 3 +-- > > mm/slob.c | 6 +++--- > > 13 files changed, 51 insertions(+), 31 deletions(-) > > [+Cc slab people, Catalin and affected subsystems' folks] > > just FYI, There is similar discussion about kmalloc caches' alignment. > https://lore.kernel.org/linux-mm/20220405135758.774016-1-catalin.marinas@arm.com/ > > It seems this is another demand for runtime resolution of slab > alignment, But slightly different from kmalloc as there is no requirement > for DMA alignment. > > > > > diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h > > index f0f1fc5d62b6..b6a7763fd5d6 100644 > > --- a/arch/arc/include/asm/cache.h > > +++ b/arch/arc/include/asm/cache.h > > @@ -55,11 +55,11 @@ > > * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses > > * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit > > * alignment for any atomic64_t embedded in buffer. > > - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed > > + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed > > * value of 4 (and not 8) in ARC ABI. > > */ > > #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC) > > -#define ARCH_SLAB_MINALIGN 8 > > +#define ARCH_SLAB_MIN_MINALIGN 8 > > #endif > > > > Why isn't it just ARCH_SLAB_MINALIGN? Because this is the minimum possible value of the minimum alignment decided at runtime. I chose to give it a different name to arch_slab_minalign() because the two have different meanings. Granted this isn't a great name because of the stuttering but hopefully it will prompt folks to investigate the meaning of this constant if necessary. > > extern int ioc_enable; > > diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h > > index e3ea34558ada..3e1018bb9805 100644 > > --- a/arch/arm/include/asm/cache.h > > +++ b/arch/arm/include/asm/cache.h > > @@ -21,7 +21,7 @@ > > * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers. > > */ > > #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) > > -#define ARCH_SLAB_MINALIGN 8 > > +#define ARCH_SLAB_MIN_MINALIGN 8 > > #endif > > > > #define __read_mostly __section(".data..read_mostly") > > diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h > > index a074459f8f2f..38f171591c3f 100644 > > --- a/arch/arm64/include/asm/cache.h > > +++ b/arch/arm64/include/asm/cache.h > > @@ -6,6 +6,7 @@ > > #define __ASM_CACHE_H > > > > #include <asm/cputype.h> > > +#include <asm/mte-def.h> > > > > #define CTR_L1IP_SHIFT 14 > > #define CTR_L1IP_MASK 3 > > @@ -49,15 +50,21 @@ > > */ > > #define ARCH_DMA_MINALIGN (128) > > > > -#ifdef CONFIG_KASAN_SW_TAGS > > -#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > > -#elif defined(CONFIG_KASAN_HW_TAGS) > > -#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE > > -#endif > > - > > #ifndef __ASSEMBLY__ > > > > #include <linux/bitops.h> > > +#include <linux/kasan-enabled.h> > > + > > +#ifdef CONFIG_KASAN_SW_TAGS > > +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > > +#elif defined(CONFIG_KASAN_HW_TAGS) > > +static inline size_t arch_slab_minalign(void) > > +{ > > + return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE : > > + __alignof__(unsigned long long); > > +} > > +#define arch_slab_minalign() arch_slab_minalign() > > +#endif > > > > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. > What about writing a new helper something like kasan_is_disabled() > instead? The decision of whether to enable KASAN is made early, before the slab allocator is initialized (start_kernel -> smp_prepare_boot_cpu -> kasan_init_hw_tags vs start_kernel -> mm_init -> kmem_cache_init). If you think about it, this needs to be the case for KASAN to operate correctly because it influences the behavior of the slab allocator via the kasan_*poison* hooks. So I don't think we can end up calling this function before then. > > #define ICACHEF_ALIASING 0 > > #define ICACHEF_VPIPT 1 > > diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h > > index 4b8b2fa78fc5..ccdbc1da3c3e 100644 > > --- a/arch/microblaze/include/asm/page.h > > +++ b/arch/microblaze/include/asm/page.h > > @@ -33,7 +33,7 @@ > > /* MS be sure that SLAB allocates aligned objects */ > > #define ARCH_DMA_MINALIGN L1_CACHE_BYTES > > > > -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES > > +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES > > > > /* > > * PAGE_OFFSET -- the first address of the first page of memory. With MMU > > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h > > index 9b58b104559e..7beb3b5d27c7 100644 > > --- a/arch/riscv/include/asm/cache.h > > +++ b/arch/riscv/include/asm/cache.h > > @@ -16,7 +16,7 @@ > > * the flat loader aligns it accordingly. > > */ > > #ifndef CONFIG_MMU > > -#define ARCH_SLAB_MINALIGN 16 > > +#define ARCH_SLAB_MIN_MINALIGN 16 > > #endif > > > > #endif /* _ASM_RISCV_CACHE_H */ > > diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h > > index e62fd0e72606..9d8cb4687b7e 100644 > > --- a/arch/sparc/include/asm/cache.h > > +++ b/arch/sparc/include/asm/cache.h > > @@ -8,7 +8,7 @@ > > #ifndef _SPARC_CACHE_H > > #define _SPARC_CACHE_H > > > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > > > > #define L1_CACHE_SHIFT 5 > > #define L1_CACHE_BYTES 32 > > diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h > > index 4489a27d527a..e3ea278e3fcf 100644 > > --- a/arch/xtensa/include/asm/processor.h > > +++ b/arch/xtensa/include/asm/processor.h > > @@ -18,7 +18,7 @@ > > #include <asm/types.h> > > #include <asm/regs.h> > > > > -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT > > +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT > > > > /* > > * User space process size: 1 GB. > > diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c > > index 626898150011..8ff1bf7d1e87 100644 > > --- a/fs/binfmt_flat.c > > +++ b/fs/binfmt_flat.c > > @@ -64,7 +64,10 @@ > > * Here we can be a bit looser than the data sections since this > > * needs to only meet arch ABI requirements. > > */ > > -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN) > > +static size_t flat_stack_align(void) > > +{ > > + return max_t(unsigned long, sizeof(void *), arch_slab_minalign()); > > +} > > > > #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */ > > #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */ > > @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start > > sp -= 2; /* argvp + envp */ > > sp -= 1; /* &argc */ > > > > - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN; > > + current->mm->start_stack = (unsigned long)sp & -flat_stack_align(); > > sp = (unsigned long __user *)current->mm->start_stack; > > > > if (put_user(bprm->argc, sp++)) > > @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm) > > #endif > > stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */ > > stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */ > > - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN); > > + stack_len = ALIGN(stack_len, flat_stack_align()); > > > > res = load_flat_file(bprm, &libinfo, 0, &stack_len); > > if (res < 0) > > diff --git a/include/crypto/hash.h b/include/crypto/hash.h > > index f140e4643949..442c290f458c 100644 > > --- a/include/crypto/hash.h > > +++ b/include/crypto/hash.h > > @@ -149,7 +149,7 @@ struct ahash_alg { > > > > struct shash_desc { > > struct crypto_shash *tfm; > > - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN); > > + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN); > > }; > > > > #define HASH_MAX_DIGESTSIZE 64 > > diff --git a/include/linux/slab.h b/include/linux/slab.h > > index 373b3ef99f4e..80e517593372 100644 > > --- a/include/linux/slab.h > > +++ b/include/linux/slab.h > > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object); > > #endif > > > > /* > > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. > > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment. > > * Intended for arches that get misalignment faults even for 64 bit integer > > * aligned buffers. > > */ > > -#ifndef ARCH_SLAB_MINALIGN > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > > +#ifndef ARCH_SLAB_MIN_MINALIGN > > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > > +#endif > > + > > +/* > > + * Arches can define this function if they want to decide the minimum slab > > + * alignment at runtime. The value returned by the function must be > > + * >= ARCH_SLAB_MIN_MINALIGN. > > + */ > > Not only the value should be bigger than or equal to ARCH_SLAB_MIN_MINALIGN, > it should be compatible with ARCH_SLAB_MIN_MINALIGN. What's the difference? Peter
On Thu, Apr 21, 2022 at 10:16:25AM -0700, Peter Collingbourne wrote: > On Thu, Apr 21, 2022 at 5:30 AM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote: > > > > On Wed, Apr 20, 2022 at 08:17:38PM -0700, Peter Collingbourne wrote: > > > When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum > > > slab alignment to 16. This happens even if MTE is not supported in > > > hardware or disabled via kasan=off, which creates an unnecessary > > > memory overhead in those cases. Eliminate this overhead by making > > > the minimum slab alignment a runtime property and only aligning to > > > 16 if KASAN is enabled at runtime. > > > > > > On a DragonBoard 845c (non-MTE hardware) with a kernel built with > > > CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android > > > boot I see the following Slab measurements in /proc/meminfo (median > > > of 3 reboots): > > > > > > Before: 169020 kB > > > After: 167304 kB > > > > > > Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead > > > Signed-off-by: Peter Collingbourne <pcc@google.com> > > > --- > > > arch/arc/include/asm/cache.h | 4 ++-- > > > arch/arm/include/asm/cache.h | 2 +- > > > arch/arm64/include/asm/cache.h | 19 +++++++++++++------ > > > arch/microblaze/include/asm/page.h | 2 +- > > > arch/riscv/include/asm/cache.h | 2 +- > > > arch/sparc/include/asm/cache.h | 2 +- > > > arch/xtensa/include/asm/processor.h | 2 +- > > > fs/binfmt_flat.c | 9 ++++++--- > > > include/crypto/hash.h | 2 +- > > > include/linux/slab.h | 22 +++++++++++++++++----- > > > mm/slab.c | 7 +++---- > > > mm/slab_common.c | 3 +-- > > > mm/slob.c | 6 +++--- > > > 13 files changed, 51 insertions(+), 31 deletions(-) > > > > [+Cc slab people, Catalin and affected subsystems' folks] > > > > just FYI, There is similar discussion about kmalloc caches' alignment. > > https://lore.kernel.org/linux-mm/20220405135758.774016-1-catalin.marinas@arm.com/ > > > > It seems this is another demand for runtime resolution of slab > > alignment, But slightly different from kmalloc as there is no requirement > > for DMA alignment. > > > > > > > > diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h > > > index f0f1fc5d62b6..b6a7763fd5d6 100644 > > > --- a/arch/arc/include/asm/cache.h > > > +++ b/arch/arc/include/asm/cache.h > > > @@ -55,11 +55,11 @@ > > > * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses > > > * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit > > > * alignment for any atomic64_t embedded in buffer. > > > - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed > > > + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed > > > * value of 4 (and not 8) in ARC ABI. > > > */ > > > #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC) > > > -#define ARCH_SLAB_MINALIGN 8 > > > +#define ARCH_SLAB_MIN_MINALIGN 8 > > > #endifh > > > > > > > Why isn't it just ARCH_SLAB_MINALIGN? > > Because this is the minimum possible value of the minimum alignment > decided at runtime. I chose to give it a different name to > arch_slab_minalign() because the two have different meanings. > > Granted this isn't a great name because of the stuttering but > hopefully it will prompt folks to investigate the meaning of this > constant if necessary. To be honest I don't care much about the name but just thought it's just better to be consistent with Catalin's series: ARCH_KMALLOC_MINALIGN for static alignment and arch_kmalloc_minalign() for (possibly bigger) alignment decided at runtime. > > > extern int ioc_enable; > > > diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h > > > index e3ea34558ada..3e1018bb9805 100644 > > > --- a/arch/arm/include/asm/cache.h > > > +++ b/arch/arm/include/asm/cache.h > > > @@ -21,7 +21,7 @@ > > > * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers. > > > */ > > > #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) > > > -#define ARCH_SLAB_MINALIGN 8 > > > +#define ARCH_SLAB_MIN_MINALIGN 8 > > > #endif > > > > > > #define __read_mostly __section(".data..read_mostly") > > > diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h > > > index a074459f8f2f..38f171591c3f 100644 > > > --- a/arch/arm64/include/asm/cache.h > > > +++ b/arch/arm64/include/asm/cache.h > > > @@ -6,6 +6,7 @@ > > > #define __ASM_CACHE_H > > > > > > #include <asm/cputype.h> > > > +#include <asm/mte-def.h> > > > > > > #define CTR_L1IP_SHIFT 14 > > > #define CTR_L1IP_MASK 3 > > > @@ -49,15 +50,21 @@ > > > */ > > > #define ARCH_DMA_MINALIGN (128) > > > > > > -#ifdef CONFIG_KASAN_SW_TAGS > > > -#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > > > -#elif defined(CONFIG_KASAN_HW_TAGS) > > > -#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE > > > -#endif > > > - > > > #ifndef __ASSEMBLY__ > > > > > > #include <linux/bitops.h> > > > +#include <linux/kasan-enabled.h> > > > + > > > +#ifdef CONFIG_KASAN_SW_TAGS > > > +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > > > +#elif defined(CONFIG_KASAN_HW_TAGS) > > > +static inline size_t arch_slab_minalign(void) > > > +{ > > > + return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE : > > > + __alignof__(unsigned long long); > > > +} > > > +#define arch_slab_minalign() arch_slab_minalign() > > > +#endif > > > > > > > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. > > What about writing a new helper something like kasan_is_disabled() > > instead? > > The decision of whether to enable KASAN is made early, before the slab > allocator is initialized (start_kernel -> smp_prepare_boot_cpu -> > kasan_init_hw_tags vs start_kernel -> mm_init -> kmem_cache_init). If > you think about it, this needs to be the case for KASAN to operate > correctly because it influences the behavior of the slab allocator via > the kasan_*poison* hooks. So I don't think we can end up calling this > function before then. Sounds not bad. I wanted to make sure the value of arch_slab_minaligned() is not changed during its execution. Just some part of me thought something like this would be more intuitive/robust. if (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF) return MTE_GRANULE_SIZE; else return __alignof__(unsigned long long); > > > #define ICACHEF_ALIASING 0 > > > #define ICACHEF_VPIPT 1 > > > diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h > > > index 4b8b2fa78fc5..ccdbc1da3c3e 100644 > > > --- a/arch/microblaze/include/asm/page.h > > > +++ b/arch/microblaze/include/asm/page.h > > > @@ -33,7 +33,7 @@ > > > /* MS be sure that SLAB allocates aligned objects */ > > > #define ARCH_DMA_MINALIGN L1_CACHE_BYTES > > > > > > -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES > > > +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES > > > > > > /* > > > * PAGE_OFFSET -- the first address of the first page of memory. With MMU > > > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h > > > index 9b58b104559e..7beb3b5d27c7 100644 > > > --- a/arch/riscv/include/asm/cache.h > > > +++ b/arch/riscv/include/asm/cache.h > > > @@ -16,7 +16,7 @@ > > > * the flat loader aligns it accordingly. > > > */ > > > #ifndef CONFIG_MMU > > > -#define ARCH_SLAB_MINALIGN 16 > > > +#define ARCH_SLAB_MIN_MINALIGN 16 > > > #endif > > > > > > #endif /* _ASM_RISCV_CACHE_H */ > > > diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h > > > index e62fd0e72606..9d8cb4687b7e 100644 > > > --- a/arch/sparc/include/asm/cache.h > > > +++ b/arch/sparc/include/asm/cache.h > > > @@ -8,7 +8,7 @@ > > > #ifndef _SPARC_CACHE_H > > > #define _SPARC_CACHE_H > > > > > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > > > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > > > > > > #define L1_CACHE_SHIFT 5 > > > #define L1_CACHE_BYTES 32 > > > diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h > > > index 4489a27d527a..e3ea278e3fcf 100644 > > > --- a/arch/xtensa/include/asm/processor.h > > > +++ b/arch/xtensa/include/asm/processor.h > > > @@ -18,7 +18,7 @@ > > > #include <asm/types.h> > > > #include <asm/regs.h> > > > > > > -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT > > > +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT > > > > > > /* > > > * User space process size: 1 GB. > > > diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c > > > index 626898150011..8ff1bf7d1e87 100644 > > > --- a/fs/binfmt_flat.c > > > +++ b/fs/binfmt_flat.c > > > @@ -64,7 +64,10 @@ > > > * Here we can be a bit looser than the data sections since this > > > * needs to only meet arch ABI requirements. > > > */ > > > -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN) > > > +static size_t flat_stack_align(void) > > > +{ > > > + return max_t(unsigned long, sizeof(void *), arch_slab_minalign()); > > > +} > > > > > > #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */ > > > #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */ > > > @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start > > > sp -= 2; /* argvp + envp */ > > > sp -= 1; /* &argc */ > > > > > > - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN; > > > + current->mm->start_stack = (unsigned long)sp & -flat_stack_align(); > > > sp = (unsigned long __user *)current->mm->start_stack; > > > > > > if (put_user(bprm->argc, sp++)) > > > @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm) > > > #endif > > > stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */ > > > stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */ > > > - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN); > > > + stack_len = ALIGN(stack_len, flat_stack_align()); > > > > > > res = load_flat_file(bprm, &libinfo, 0, &stack_len); > > > if (res < 0) > > > diff --git a/include/crypto/hash.h b/include/crypto/hash.h > > > index f140e4643949..442c290f458c 100644 > > > --- a/include/crypto/hash.h > > > +++ b/include/crypto/hash.h > > > @@ -149,7 +149,7 @@ struct ahash_alg { > > > > > > struct shash_desc { > > > struct crypto_shash *tfm; > > > - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN); > > > + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN); > > > }; > > > > > > #define HASH_MAX_DIGESTSIZE 64 > > > diff --git a/include/linux/slab.h b/include/linux/slab.h > > > index 373b3ef99f4e..80e517593372 100644 > > > --- a/include/linux/slab.h > > > +++ b/include/linux/slab.h > > > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object); > > > #endif > > > > > > /* > > > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. > > > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment. > > > * Intended for arches that get misalignment faults even for 64 bit integer > > > * aligned buffers. > > > */ > > > -#ifndef ARCH_SLAB_MINALIGN > > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > > > +#ifndef ARCH_SLAB_MIN_MINALIGN > > > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > > > +#endif > > > + > > > +/* > > > + * Arches can define this function if they want to decide the minimum slab > > > + * alignment at runtime. The value returned by the function must be > > > + * >= ARCH_SLAB_MIN_MINALIGN. > > > + */ > > > > Not only the value should be bigger than or equal to ARCH_SLAB_MIN_MINALIGN, > > it should be compatible with ARCH_SLAB_MIN_MINALIGN. > > What's the difference? > 231 /* 232 * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned 233 * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN 234 * aligned pointers. 235 */ 236 #define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN) 237 #define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MIN_MINALIGN) 238 #define __assume_page_alignment __assume_aligned(PAGE_SIZE) I mean actual slab object size should be both ARCH_SLAB_MIN_MINALIGN-aligned and arch_slab_minalign()-aligned. Otherwise we are lying to the compiler. It's okay If we use just power-of-two alignment. But adding a comment wouldn't harm :) Thank you for the work. I think the patch makes sense as usually people don't build and install their kernel for arm64 machines. > Peter
On Fri, Apr 22, 2022 at 2:39 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote: > > > > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. > > > What about writing a new helper something like kasan_is_disabled() > > > instead? > > > > The decision of whether to enable KASAN is made early, before the slab > > allocator is initialized (start_kernel -> smp_prepare_boot_cpu -> > > kasan_init_hw_tags vs start_kernel -> mm_init -> kmem_cache_init). If > > you think about it, this needs to be the case for KASAN to operate > > correctly because it influences the behavior of the slab allocator via > > the kasan_*poison* hooks. So I don't think we can end up calling this > > function before then. > > Sounds not bad. I wanted to make sure the value of arch_slab_minaligned() > is not changed during its execution. > > Just some part of me thought something like this would be more > intuitive/robust. > > if (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF) > return MTE_GRANULE_SIZE; > else > return __alignof__(unsigned long long); Hi Hyeonggon, We could add and use kasan_hw_rags_requested(), which would return (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF). However, I'm not sure we will get a fully static behavior: systems_supports_mte() also only starts returning proper result at some point during CPU bring-up if I'm not mistaken. Thanks!
On 4/22/22 14:39, Hyeonggon Yoo wrote: > On Thu, Apr 21, 2022 at 10:16:25AM -0700, Peter Collingbourne wrote: >> On Thu, Apr 21, 2022 at 5:30 AM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote: >> > >> > On Wed, Apr 20, 2022 at 08:17:38PM -0700, Peter Collingbourne wrote: >> > > When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum >> > > slab alignment to 16. This happens even if MTE is not supported in >> > > hardware or disabled via kasan=off, which creates an unnecessary >> > > memory overhead in those cases. Eliminate this overhead by making >> > > the minimum slab alignment a runtime property and only aligning to >> > > 16 if KASAN is enabled at runtime. >> > > >> > > On a DragonBoard 845c (non-MTE hardware) with a kernel built with >> > > CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android >> > > boot I see the following Slab measurements in /proc/meminfo (median >> > > of 3 reboots): >> > > >> > > Before: 169020 kB >> > > After: 167304 kB >> > > >> > > Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead >> > > Signed-off-by: Peter Collingbourne <pcc@google.com> >> > > --- >> > > arch/arc/include/asm/cache.h | 4 ++-- >> > > arch/arm/include/asm/cache.h | 2 +- >> > > arch/arm64/include/asm/cache.h | 19 +++++++++++++------ >> > > arch/microblaze/include/asm/page.h | 2 +- >> > > arch/riscv/include/asm/cache.h | 2 +- >> > > arch/sparc/include/asm/cache.h | 2 +- >> > > arch/xtensa/include/asm/processor.h | 2 +- >> > > fs/binfmt_flat.c | 9 ++++++--- >> > > include/crypto/hash.h | 2 +- >> > > include/linux/slab.h | 22 +++++++++++++++++----- >> > > mm/slab.c | 7 +++---- >> > > mm/slab_common.c | 3 +-- >> > > mm/slob.c | 6 +++--- >> > > 13 files changed, 51 insertions(+), 31 deletions(-) >> > >> > [+Cc slab people, Catalin and affected subsystems' folks] >> > >> > just FYI, There is similar discussion about kmalloc caches' alignment. >> > https://lore.kernel.org/linux-mm/20220405135758.774016-1-catalin.marinas@arm.com/ >> > >> > It seems this is another demand for runtime resolution of slab >> > alignment, But slightly different from kmalloc as there is no requirement >> > for DMA alignment. >> > >> > > >> > > diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h >> > > index f0f1fc5d62b6..b6a7763fd5d6 100644 >> > > --- a/arch/arc/include/asm/cache.h >> > > +++ b/arch/arc/include/asm/cache.h >> > > @@ -55,11 +55,11 @@ >> > > * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses >> > > * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit >> > > * alignment for any atomic64_t embedded in buffer. >> > > - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed >> > > + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed >> > > * value of 4 (and not 8) in ARC ABI. >> > > */ >> > > #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC) >> > > -#define ARCH_SLAB_MINALIGN 8 >> > > +#define ARCH_SLAB_MIN_MINALIGN 8 >> > > #endifh >> > > >> > >> > Why isn't it just ARCH_SLAB_MINALIGN? >> >> Because this is the minimum possible value of the minimum alignment >> decided at runtime. I chose to give it a different name to >> arch_slab_minalign() because the two have different meanings. >> >> Granted this isn't a great name because of the stuttering but >> hopefully it will prompt folks to investigate the meaning of this >> constant if necessary. > > To be honest I don't care much about the name but just thought it's just better > to be consistent with Catalin's series: ARCH_KMALLOC_MINALIGN for static > alignment and arch_kmalloc_minalign() for (possibly bigger) alignment decided > at runtime. Agree it should be consistent, one way or another. I would (not overly strongly) prefer Catalin's approach as it's less churn. The name ARCH_SLAB_MINALIGN is not wrong as the actual alignment can be only bigger than that (or equal). Realistically it seems only slab internals are going to use arch_kmalloc_minalign(), so there shouldn't be too much need of "prompt folks to investigate". >> > > extern int ioc_enable; >> > > diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h >> > > index e3ea34558ada..3e1018bb9805 100644 >> > > --- a/arch/arm/include/asm/cache.h >> > > +++ b/arch/arm/include/asm/cache.h >> > > @@ -21,7 +21,7 @@ >> > > * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers. >> > > */ >> > > #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) >> > > -#define ARCH_SLAB_MINALIGN 8 >> > > +#define ARCH_SLAB_MIN_MINALIGN 8 >> > > #endif >> > > >> > > #define __read_mostly __section(".data..read_mostly") >> > > diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h >> > > index a074459f8f2f..38f171591c3f 100644 >> > > --- a/arch/arm64/include/asm/cache.h >> > > +++ b/arch/arm64/include/asm/cache.h >> > > @@ -6,6 +6,7 @@ >> > > #define __ASM_CACHE_H >> > > >> > > #include <asm/cputype.h> >> > > +#include <asm/mte-def.h> >> > > >> > > #define CTR_L1IP_SHIFT 14 >> > > #define CTR_L1IP_MASK 3 >> > > @@ -49,15 +50,21 @@ >> > > */ >> > > #define ARCH_DMA_MINALIGN (128) >> > > >> > > -#ifdef CONFIG_KASAN_SW_TAGS >> > > -#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) >> > > -#elif defined(CONFIG_KASAN_HW_TAGS) >> > > -#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE >> > > -#endif >> > > - >> > > #ifndef __ASSEMBLY__ >> > > >> > > #include <linux/bitops.h> >> > > +#include <linux/kasan-enabled.h> >> > > + >> > > +#ifdef CONFIG_KASAN_SW_TAGS >> > > +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) >> > > +#elif defined(CONFIG_KASAN_HW_TAGS) >> > > +static inline size_t arch_slab_minalign(void) >> > > +{ >> > > + return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE : >> > > + __alignof__(unsigned long long); >> > > +} >> > > +#define arch_slab_minalign() arch_slab_minalign() >> > > +#endif >> > > >> > >> > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. >> > What about writing a new helper something like kasan_is_disabled() >> > instead? >> >> The decision of whether to enable KASAN is made early, before the slab >> allocator is initialized (start_kernel -> smp_prepare_boot_cpu -> >> kasan_init_hw_tags vs start_kernel -> mm_init -> kmem_cache_init). If >> you think about it, this needs to be the case for KASAN to operate >> correctly because it influences the behavior of the slab allocator via >> the kasan_*poison* hooks. So I don't think we can end up calling this >> function before then. > > Sounds not bad. I wanted to make sure the value of arch_slab_minaligned() > is not changed during its execution. > > Just some part of me thought something like this would be more > intuitive/robust. > > if (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF) > return MTE_GRANULE_SIZE; > else > return __alignof__(unsigned long long); Let's see if kasan or arm folks have an opinion here. > >> > > #define ICACHEF_ALIASING 0 >> > > #define ICACHEF_VPIPT 1 >> > > diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h >> > > index 4b8b2fa78fc5..ccdbc1da3c3e 100644 >> > > --- a/arch/microblaze/include/asm/page.h >> > > +++ b/arch/microblaze/include/asm/page.h >> > > @@ -33,7 +33,7 @@ >> > > /* MS be sure that SLAB allocates aligned objects */ >> > > #define ARCH_DMA_MINALIGN L1_CACHE_BYTES >> > > >> > > -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES >> > > +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES >> > > >> > > /* >> > > * PAGE_OFFSET -- the first address of the first page of memory. With MMU >> > > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h >> > > index 9b58b104559e..7beb3b5d27c7 100644 >> > > --- a/arch/riscv/include/asm/cache.h >> > > +++ b/arch/riscv/include/asm/cache.h >> > > @@ -16,7 +16,7 @@ >> > > * the flat loader aligns it accordingly. >> > > */ >> > > #ifndef CONFIG_MMU >> > > -#define ARCH_SLAB_MINALIGN 16 >> > > +#define ARCH_SLAB_MIN_MINALIGN 16 >> > > #endif >> > > >> > > #endif /* _ASM_RISCV_CACHE_H */ >> > > diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h >> > > index e62fd0e72606..9d8cb4687b7e 100644 >> > > --- a/arch/sparc/include/asm/cache.h >> > > +++ b/arch/sparc/include/asm/cache.h >> > > @@ -8,7 +8,7 @@ >> > > #ifndef _SPARC_CACHE_H >> > > #define _SPARC_CACHE_H >> > > >> > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) >> > > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) >> > > >> > > #define L1_CACHE_SHIFT 5 >> > > #define L1_CACHE_BYTES 32 >> > > diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h >> > > index 4489a27d527a..e3ea278e3fcf 100644 >> > > --- a/arch/xtensa/include/asm/processor.h >> > > +++ b/arch/xtensa/include/asm/processor.h >> > > @@ -18,7 +18,7 @@ >> > > #include <asm/types.h> >> > > #include <asm/regs.h> >> > > >> > > -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT >> > > +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT >> > > >> > > /* >> > > * User space process size: 1 GB. >> > > diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c >> > > index 626898150011..8ff1bf7d1e87 100644 >> > > --- a/fs/binfmt_flat.c >> > > +++ b/fs/binfmt_flat.c >> > > @@ -64,7 +64,10 @@ >> > > * Here we can be a bit looser than the data sections since this >> > > * needs to only meet arch ABI requirements. >> > > */ >> > > -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN) >> > > +static size_t flat_stack_align(void) >> > > +{ >> > > + return max_t(unsigned long, sizeof(void *), arch_slab_minalign()); >> > > +} I think this might not be necessary at all. There doesn't seem to be actual connection to the slab+kasan constraints here. My brief digging into git blame suggest they just used the ARCH_SLAB_MINALIGN constant because it existed, e.g. commit 2952095c6b2ee includes in changelog "Arguably, this is kind of hokey that the FLAT is semi-abusing defines it shouldn't." So, there shouldn't be a reason to increase this due to KASAN/MTE granule size, it was done unnecessarily as a side-effect before (AFAIU it shouldn't have caused existing userspace binaries to break, but maybe in some corner case it could?), and if this patch leaves out the binfmt_flat changes, the alignment will be (IMHO correctly) decreased again. >> > > >> > > #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */ >> > > #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */ >> > > @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start >> > > sp -= 2; /* argvp + envp */ >> > > sp -= 1; /* &argc */ >> > > >> > > - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN; >> > > + current->mm->start_stack = (unsigned long)sp & -flat_stack_align(); >> > > sp = (unsigned long __user *)current->mm->start_stack; >> > > >> > > if (put_user(bprm->argc, sp++)) >> > > @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm) >> > > #endif >> > > stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */ >> > > stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */ >> > > - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN); >> > > + stack_len = ALIGN(stack_len, flat_stack_align()); >> > > >> > > res = load_flat_file(bprm, &libinfo, 0, &stack_len); >> > > if (res < 0) >> > > diff --git a/include/crypto/hash.h b/include/crypto/hash.h >> > > index f140e4643949..442c290f458c 100644 >> > > --- a/include/crypto/hash.h >> > > +++ b/include/crypto/hash.h >> > > @@ -149,7 +149,7 @@ struct ahash_alg { >> > > >> > > struct shash_desc { >> > > struct crypto_shash *tfm; >> > > - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN); >> > > + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN); >> > > }; >> > > >> > > #define HASH_MAX_DIGESTSIZE 64 >> > > diff --git a/include/linux/slab.h b/include/linux/slab.h >> > > index 373b3ef99f4e..80e517593372 100644 >> > > --- a/include/linux/slab.h >> > > +++ b/include/linux/slab.h >> > > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object); >> > > #endif >> > > >> > > /* >> > > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. >> > > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment. >> > > * Intended for arches that get misalignment faults even for 64 bit integer >> > > * aligned buffers. >> > > */ >> > > -#ifndef ARCH_SLAB_MINALIGN >> > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) >> > > +#ifndef ARCH_SLAB_MIN_MINALIGN >> > > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) >> > > +#endif >> > > + >> > > +/* >> > > + * Arches can define this function if they want to decide the minimum slab >> > > + * alignment at runtime. The value returned by the function must be >> > > + * >= ARCH_SLAB_MIN_MINALIGN. >> > > + */ >> > >> > Not only the value should be bigger than or equal to ARCH_SLAB_MIN_MINALIGN, >> > it should be compatible with ARCH_SLAB_MIN_MINALIGN. >> >> What's the difference? >> > > 231 /* > 232 * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned > 233 * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN > 234 * aligned pointers. > 235 */ > 236 #define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN) > 237 #define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MIN_MINALIGN) > 238 #define __assume_page_alignment __assume_aligned(PAGE_SIZE) > > I mean actual slab object size should be both ARCH_SLAB_MIN_MINALIGN-aligned and > arch_slab_minalign()-aligned. Otherwise we are lying to the compiler. > > It's okay If we use just power-of-two alignment. > But adding a comment wouldn't harm :) Agreed, technically it's not ">=ARCH_SLAB_MIN_MINALIGN", but "a least common multiple of ARCH_SLAB_MIN_MINALIGN and whatever the other alignment requirements arch_slab_minalign() wants to guarantee". But AFAIK in practice these constraints are always power-of-two. > Thank you for the work. I think the patch makes sense as usually people > don't build and install their kernel for arm64 machines. > >> Peter >
On Fri, Apr 22, 2022 at 9:09 AM Andrey Konovalov <andreyknvl@gmail.com> wrote: > > On Fri, Apr 22, 2022 at 2:39 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote: > > > > > > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. > > > > What about writing a new helper something like kasan_is_disabled() > > > > instead? > > > > > > The decision of whether to enable KASAN is made early, before the slab > > > allocator is initialized (start_kernel -> smp_prepare_boot_cpu -> > > > kasan_init_hw_tags vs start_kernel -> mm_init -> kmem_cache_init). If > > > you think about it, this needs to be the case for KASAN to operate > > > correctly because it influences the behavior of the slab allocator via > > > the kasan_*poison* hooks. So I don't think we can end up calling this > > > function before then. > > > > Sounds not bad. I wanted to make sure the value of arch_slab_minaligned() > > is not changed during its execution. > > > > Just some part of me thought something like this would be more > > intuitive/robust. > > > > if (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF) > > return MTE_GRANULE_SIZE; > > else > > return __alignof__(unsigned long long); > > Hi Hyeonggon, > > We could add and use kasan_hw_rags_requested(), which would return > (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF). > > However, I'm not sure we will get a fully static behavior: > systems_supports_mte() also only starts returning proper result at > some point during CPU bring-up if I'm not mistaken. > > Thanks! Yes, either way we are going to rely on something that hasn't obviously been initialized yet, so I think we should stick with what I have since it's used by the rest of the KASAN code as well. Peter
On Fri, Apr 22, 2022 at 9:19 AM Vlastimil Babka <vbabka@suse.cz> wrote: > > On 4/22/22 14:39, Hyeonggon Yoo wrote: > > On Thu, Apr 21, 2022 at 10:16:25AM -0700, Peter Collingbourne wrote: > >> On Thu, Apr 21, 2022 at 5:30 AM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote: > >> > > >> > On Wed, Apr 20, 2022 at 08:17:38PM -0700, Peter Collingbourne wrote: > >> > > When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum > >> > > slab alignment to 16. This happens even if MTE is not supported in > >> > > hardware or disabled via kasan=off, which creates an unnecessary > >> > > memory overhead in those cases. Eliminate this overhead by making > >> > > the minimum slab alignment a runtime property and only aligning to > >> > > 16 if KASAN is enabled at runtime. > >> > > > >> > > On a DragonBoard 845c (non-MTE hardware) with a kernel built with > >> > > CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android > >> > > boot I see the following Slab measurements in /proc/meminfo (median > >> > > of 3 reboots): > >> > > > >> > > Before: 169020 kB > >> > > After: 167304 kB > >> > > > >> > > Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead > >> > > Signed-off-by: Peter Collingbourne <pcc@google.com> > >> > > --- > >> > > arch/arc/include/asm/cache.h | 4 ++-- > >> > > arch/arm/include/asm/cache.h | 2 +- > >> > > arch/arm64/include/asm/cache.h | 19 +++++++++++++------ > >> > > arch/microblaze/include/asm/page.h | 2 +- > >> > > arch/riscv/include/asm/cache.h | 2 +- > >> > > arch/sparc/include/asm/cache.h | 2 +- > >> > > arch/xtensa/include/asm/processor.h | 2 +- > >> > > fs/binfmt_flat.c | 9 ++++++--- > >> > > include/crypto/hash.h | 2 +- > >> > > include/linux/slab.h | 22 +++++++++++++++++----- > >> > > mm/slab.c | 7 +++---- > >> > > mm/slab_common.c | 3 +-- > >> > > mm/slob.c | 6 +++--- > >> > > 13 files changed, 51 insertions(+), 31 deletions(-) > >> > > >> > [+Cc slab people, Catalin and affected subsystems' folks] > >> > > >> > just FYI, There is similar discussion about kmalloc caches' alignment. > >> > https://lore.kernel.org/linux-mm/20220405135758.774016-1-catalin.marinas@arm.com/ > >> > > >> > It seems this is another demand for runtime resolution of slab > >> > alignment, But slightly different from kmalloc as there is no requirement > >> > for DMA alignment. > >> > > >> > > > >> > > diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h > >> > > index f0f1fc5d62b6..b6a7763fd5d6 100644 > >> > > --- a/arch/arc/include/asm/cache.h > >> > > +++ b/arch/arc/include/asm/cache.h > >> > > @@ -55,11 +55,11 @@ > >> > > * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses > >> > > * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit > >> > > * alignment for any atomic64_t embedded in buffer. > >> > > - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed > >> > > + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed > >> > > * value of 4 (and not 8) in ARC ABI. > >> > > */ > >> > > #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC) > >> > > -#define ARCH_SLAB_MINALIGN 8 > >> > > +#define ARCH_SLAB_MIN_MINALIGN 8 > >> > > #endifh > >> > > > >> > > >> > Why isn't it just ARCH_SLAB_MINALIGN? > >> > >> Because this is the minimum possible value of the minimum alignment > >> decided at runtime. I chose to give it a different name to > >> arch_slab_minalign() because the two have different meanings. > >> > >> Granted this isn't a great name because of the stuttering but > >> hopefully it will prompt folks to investigate the meaning of this > >> constant if necessary. > > > > To be honest I don't care much about the name but just thought it's just better > > to be consistent with Catalin's series: ARCH_KMALLOC_MINALIGN for static > > alignment and arch_kmalloc_minalign() for (possibly bigger) alignment decided > > at runtime. > > Agree it should be consistent, one way or another. I would (not overly > strongly) prefer Catalin's approach as it's less churn. The name > ARCH_SLAB_MINALIGN is not wrong as the actual alignment can be only bigger > than that (or equal). > Realistically it seems only slab internals are going to use > arch_kmalloc_minalign(), so there shouldn't be too much need of "prompt > folks to investigate". No strong opinion, so I'll change it back to ARCH_SLAB_MINALIGN then. > >> > > extern int ioc_enable; > >> > > diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h > >> > > index e3ea34558ada..3e1018bb9805 100644 > >> > > --- a/arch/arm/include/asm/cache.h > >> > > +++ b/arch/arm/include/asm/cache.h > >> > > @@ -21,7 +21,7 @@ > >> > > * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers. > >> > > */ > >> > > #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) > >> > > -#define ARCH_SLAB_MINALIGN 8 > >> > > +#define ARCH_SLAB_MIN_MINALIGN 8 > >> > > #endif > >> > > > >> > > #define __read_mostly __section(".data..read_mostly") > >> > > diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h > >> > > index a074459f8f2f..38f171591c3f 100644 > >> > > --- a/arch/arm64/include/asm/cache.h > >> > > +++ b/arch/arm64/include/asm/cache.h > >> > > @@ -6,6 +6,7 @@ > >> > > #define __ASM_CACHE_H > >> > > > >> > > #include <asm/cputype.h> > >> > > +#include <asm/mte-def.h> > >> > > > >> > > #define CTR_L1IP_SHIFT 14 > >> > > #define CTR_L1IP_MASK 3 > >> > > @@ -49,15 +50,21 @@ > >> > > */ > >> > > #define ARCH_DMA_MINALIGN (128) > >> > > > >> > > -#ifdef CONFIG_KASAN_SW_TAGS > >> > > -#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > >> > > -#elif defined(CONFIG_KASAN_HW_TAGS) > >> > > -#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE > >> > > -#endif > >> > > - > >> > > #ifndef __ASSEMBLY__ > >> > > > >> > > #include <linux/bitops.h> > >> > > +#include <linux/kasan-enabled.h> > >> > > + > >> > > +#ifdef CONFIG_KASAN_SW_TAGS > >> > > +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > >> > > +#elif defined(CONFIG_KASAN_HW_TAGS) > >> > > +static inline size_t arch_slab_minalign(void) > >> > > +{ > >> > > + return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE : > >> > > + __alignof__(unsigned long long); > >> > > +} > >> > > +#define arch_slab_minalign() arch_slab_minalign() > >> > > +#endif > >> > > > >> > > >> > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. > >> > What about writing a new helper something like kasan_is_disabled() > >> > instead? > >> > >> The decision of whether to enable KASAN is made early, before the slab > >> allocator is initialized (start_kernel -> smp_prepare_boot_cpu -> > >> kasan_init_hw_tags vs start_kernel -> mm_init -> kmem_cache_init). If > >> you think about it, this needs to be the case for KASAN to operate > >> correctly because it influences the behavior of the slab allocator via > >> the kasan_*poison* hooks. So I don't think we can end up calling this > >> function before then. > > > > Sounds not bad. I wanted to make sure the value of arch_slab_minaligned() > > is not changed during its execution. > > > > Just some part of me thought something like this would be more > > intuitive/robust. > > > > if (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF) > > return MTE_GRANULE_SIZE; > > else > > return __alignof__(unsigned long long); > > Let's see if kasan or arm folks have an opinion here. > > > > >> > > #define ICACHEF_ALIASING 0 > >> > > #define ICACHEF_VPIPT 1 > >> > > diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h > >> > > index 4b8b2fa78fc5..ccdbc1da3c3e 100644 > >> > > --- a/arch/microblaze/include/asm/page.h > >> > > +++ b/arch/microblaze/include/asm/page.h > >> > > @@ -33,7 +33,7 @@ > >> > > /* MS be sure that SLAB allocates aligned objects */ > >> > > #define ARCH_DMA_MINALIGN L1_CACHE_BYTES > >> > > > >> > > -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES > >> > > +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES > >> > > > >> > > /* > >> > > * PAGE_OFFSET -- the first address of the first page of memory. With MMU > >> > > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h > >> > > index 9b58b104559e..7beb3b5d27c7 100644 > >> > > --- a/arch/riscv/include/asm/cache.h > >> > > +++ b/arch/riscv/include/asm/cache.h > >> > > @@ -16,7 +16,7 @@ > >> > > * the flat loader aligns it accordingly. > >> > > */ > >> > > #ifndef CONFIG_MMU > >> > > -#define ARCH_SLAB_MINALIGN 16 > >> > > +#define ARCH_SLAB_MIN_MINALIGN 16 > >> > > #endif > >> > > > >> > > #endif /* _ASM_RISCV_CACHE_H */ > >> > > diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h > >> > > index e62fd0e72606..9d8cb4687b7e 100644 > >> > > --- a/arch/sparc/include/asm/cache.h > >> > > +++ b/arch/sparc/include/asm/cache.h > >> > > @@ -8,7 +8,7 @@ > >> > > #ifndef _SPARC_CACHE_H > >> > > #define _SPARC_CACHE_H > >> > > > >> > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > >> > > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > >> > > > >> > > #define L1_CACHE_SHIFT 5 > >> > > #define L1_CACHE_BYTES 32 > >> > > diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h > >> > > index 4489a27d527a..e3ea278e3fcf 100644 > >> > > --- a/arch/xtensa/include/asm/processor.h > >> > > +++ b/arch/xtensa/include/asm/processor.h > >> > > @@ -18,7 +18,7 @@ > >> > > #include <asm/types.h> > >> > > #include <asm/regs.h> > >> > > > >> > > -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT > >> > > +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT > >> > > > >> > > /* > >> > > * User space process size: 1 GB. > >> > > diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c > >> > > index 626898150011..8ff1bf7d1e87 100644 > >> > > --- a/fs/binfmt_flat.c > >> > > +++ b/fs/binfmt_flat.c > >> > > @@ -64,7 +64,10 @@ > >> > > * Here we can be a bit looser than the data sections since this > >> > > * needs to only meet arch ABI requirements. > >> > > */ > >> > > -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN) > >> > > +static size_t flat_stack_align(void) > >> > > +{ > >> > > + return max_t(unsigned long, sizeof(void *), arch_slab_minalign()); > >> > > +} > > I think this might not be necessary at all. There doesn't seem to be actual > connection to the slab+kasan constraints here. My brief digging into git > blame suggest they just used the ARCH_SLAB_MINALIGN constant because it > existed, e.g. commit 2952095c6b2ee includes in changelog "Arguably, this is > kind of hokey that the FLAT is semi-abusing defines it shouldn't." > So, there shouldn't be a reason to increase this due to KASAN/MTE granule > size, it was done unnecessarily as a side-effect before (AFAIU it shouldn't > have caused existing userspace binaries to break, but maybe in some corner > case it could?), and if this patch leaves out the binfmt_flat changes, the > alignment will be (IMHO correctly) decreased again. Okay, I'll revert this part. > >> > > > >> > > #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */ > >> > > #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */ > >> > > @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start > >> > > sp -= 2; /* argvp + envp */ > >> > > sp -= 1; /* &argc */ > >> > > > >> > > - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN; > >> > > + current->mm->start_stack = (unsigned long)sp & -flat_stack_align(); > >> > > sp = (unsigned long __user *)current->mm->start_stack; > >> > > > >> > > if (put_user(bprm->argc, sp++)) > >> > > @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm) > >> > > #endif > >> > > stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */ > >> > > stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */ > >> > > - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN); > >> > > + stack_len = ALIGN(stack_len, flat_stack_align()); > >> > > > >> > > res = load_flat_file(bprm, &libinfo, 0, &stack_len); > >> > > if (res < 0) > >> > > diff --git a/include/crypto/hash.h b/include/crypto/hash.h > >> > > index f140e4643949..442c290f458c 100644 > >> > > --- a/include/crypto/hash.h > >> > > +++ b/include/crypto/hash.h > >> > > @@ -149,7 +149,7 @@ struct ahash_alg { > >> > > > >> > > struct shash_desc { > >> > > struct crypto_shash *tfm; > >> > > - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN); > >> > > + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN); > >> > > }; > >> > > > >> > > #define HASH_MAX_DIGESTSIZE 64 > >> > > diff --git a/include/linux/slab.h b/include/linux/slab.h > >> > > index 373b3ef99f4e..80e517593372 100644 > >> > > --- a/include/linux/slab.h > >> > > +++ b/include/linux/slab.h > >> > > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object); > >> > > #endif > >> > > > >> > > /* > >> > > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. > >> > > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment. > >> > > * Intended for arches that get misalignment faults even for 64 bit integer > >> > > * aligned buffers. > >> > > */ > >> > > -#ifndef ARCH_SLAB_MINALIGN > >> > > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) > >> > > +#ifndef ARCH_SLAB_MIN_MINALIGN > >> > > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) > >> > > +#endif > >> > > + > >> > > +/* > >> > > + * Arches can define this function if they want to decide the minimum slab > >> > > + * alignment at runtime. The value returned by the function must be > >> > > + * >= ARCH_SLAB_MIN_MINALIGN. > >> > > + */ > >> > > >> > Not only the value should be bigger than or equal to ARCH_SLAB_MIN_MINALIGN, > >> > it should be compatible with ARCH_SLAB_MIN_MINALIGN. > >> > >> What's the difference? > >> > > > > 231 /* > > 232 * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned > > 233 * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN > > 234 * aligned pointers. > > 235 */ > > 236 #define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN) > > 237 #define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MIN_MINALIGN) > > 238 #define __assume_page_alignment __assume_aligned(PAGE_SIZE) > > > > I mean actual slab object size should be both ARCH_SLAB_MIN_MINALIGN-aligned and > > arch_slab_minalign()-aligned. Otherwise we are lying to the compiler. > > > > It's okay If we use just power-of-two alignment. > > But adding a comment wouldn't harm :) > > Agreed, technically it's not ">=ARCH_SLAB_MIN_MINALIGN", but "a least common > multiple of ARCH_SLAB_MIN_MINALIGN and whatever the other alignment > requirements arch_slab_minalign() wants to guarantee". But AFAIK in practice > these constraints are always power-of-two. I think it's pretty much assumed that alignments are a power of two, so from that viewpoint it's enough to say that it must be >=ARCH_SLAB_MIN_MINALIGN. I guess I'll change the comment to say that it must return a power of two since there's no reason not to. Peter
On Fri, Apr 22, 2022 at 10:40:08AM -0700, Peter Collingbourne wrote: > On Fri, Apr 22, 2022 at 9:09 AM Andrey Konovalov <andreyknvl@gmail.com> wrote: > > > > On Fri, Apr 22, 2022 at 2:39 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote: > > > > > > > > kasan_hw_tags_enabled() is also false when kasan is just not initialized yet. > > > > > What about writing a new helper something like kasan_is_disabled() > > > > > instead? > > > > > > > > The decision of whether to enable KASAN is made early, before the slab > > > > allocator is initialized (start_kernel -> smp_prepare_boot_cpu -> > > > > kasan_init_hw_tags vs start_kernel -> mm_init -> kmem_cache_init). If > > > > you think about it, this needs to be the case for KASAN to operate > > > > correctly because it influences the behavior of the slab allocator via > > > > the kasan_*poison* hooks. So I don't think we can end up calling this > > > > function before then. > > > > > > Sounds not bad. I wanted to make sure the value of arch_slab_minaligned() > > > is not changed during its execution. > > > > > > Just some part of me thought something like this would be more > > > intuitive/robust. > > > > > > if (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF) > > > return MTE_GRANULE_SIZE; > > > else > > > return __alignof__(unsigned long long); > > > > Hi Hyeonggon, > > > > We could add and use kasan_hw_rags_requested(), which would return > > (systems_supports_mte() && kasan_arg != KASAN_ARG_OFF). > > > > However, I'm not sure we will get a fully static behavior: > > systems_supports_mte() also only starts returning proper result at > > some point during CPU bring-up if I'm not mistaken. > > > > Thanks! > > Yes, either way we are going to rely on something that hasn't > obviously been initialized yet, so I think we should stick with what I > have since it's used by the rest of the KASAN code as well. > Okay then we should anyway rely on something not initialized at early stage of boot process. And I don't expect much problem on current version. Thanks! > Peter
diff --git a/arch/arc/include/asm/cache.h b/arch/arc/include/asm/cache.h index f0f1fc5d62b6..b6a7763fd5d6 100644 --- a/arch/arc/include/asm/cache.h +++ b/arch/arc/include/asm/cache.h @@ -55,11 +55,11 @@ * Make sure slab-allocated buffers are 64-bit aligned when atomic64_t uses * ARCv2 64-bit atomics (LLOCKD/SCONDD). This guarantess runtime 64-bit * alignment for any atomic64_t embedded in buffer. - * Default ARCH_SLAB_MINALIGN is __alignof__(long long) which has a relaxed + * Default ARCH_SLAB_MIN_MINALIGN is __alignof__(long long) which has a relaxed * value of 4 (and not 8) in ARC ABI. */ #if defined(CONFIG_ARC_HAS_LL64) && defined(CONFIG_ARC_HAS_LLSC) -#define ARCH_SLAB_MINALIGN 8 +#define ARCH_SLAB_MIN_MINALIGN 8 #endif extern int ioc_enable; diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h index e3ea34558ada..3e1018bb9805 100644 --- a/arch/arm/include/asm/cache.h +++ b/arch/arm/include/asm/cache.h @@ -21,7 +21,7 @@ * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers. */ #if defined(CONFIG_AEABI) && (__LINUX_ARM_ARCH__ >= 5) -#define ARCH_SLAB_MINALIGN 8 +#define ARCH_SLAB_MIN_MINALIGN 8 #endif #define __read_mostly __section(".data..read_mostly") diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h index a074459f8f2f..38f171591c3f 100644 --- a/arch/arm64/include/asm/cache.h +++ b/arch/arm64/include/asm/cache.h @@ -6,6 +6,7 @@ #define __ASM_CACHE_H #include <asm/cputype.h> +#include <asm/mte-def.h> #define CTR_L1IP_SHIFT 14 #define CTR_L1IP_MASK 3 @@ -49,15 +50,21 @@ */ #define ARCH_DMA_MINALIGN (128) -#ifdef CONFIG_KASAN_SW_TAGS -#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) -#elif defined(CONFIG_KASAN_HW_TAGS) -#define ARCH_SLAB_MINALIGN MTE_GRANULE_SIZE -#endif - #ifndef __ASSEMBLY__ #include <linux/bitops.h> +#include <linux/kasan-enabled.h> + +#ifdef CONFIG_KASAN_SW_TAGS +#define ARCH_SLAB_MIN_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) +#elif defined(CONFIG_KASAN_HW_TAGS) +static inline size_t arch_slab_minalign(void) +{ + return kasan_hw_tags_enabled() ? MTE_GRANULE_SIZE : + __alignof__(unsigned long long); +} +#define arch_slab_minalign() arch_slab_minalign() +#endif #define ICACHEF_ALIASING 0 #define ICACHEF_VPIPT 1 diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h index 4b8b2fa78fc5..ccdbc1da3c3e 100644 --- a/arch/microblaze/include/asm/page.h +++ b/arch/microblaze/include/asm/page.h @@ -33,7 +33,7 @@ /* MS be sure that SLAB allocates aligned objects */ #define ARCH_DMA_MINALIGN L1_CACHE_BYTES -#define ARCH_SLAB_MINALIGN L1_CACHE_BYTES +#define ARCH_SLAB_MIN_MINALIGN L1_CACHE_BYTES /* * PAGE_OFFSET -- the first address of the first page of memory. With MMU diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h index 9b58b104559e..7beb3b5d27c7 100644 --- a/arch/riscv/include/asm/cache.h +++ b/arch/riscv/include/asm/cache.h @@ -16,7 +16,7 @@ * the flat loader aligns it accordingly. */ #ifndef CONFIG_MMU -#define ARCH_SLAB_MINALIGN 16 +#define ARCH_SLAB_MIN_MINALIGN 16 #endif #endif /* _ASM_RISCV_CACHE_H */ diff --git a/arch/sparc/include/asm/cache.h b/arch/sparc/include/asm/cache.h index e62fd0e72606..9d8cb4687b7e 100644 --- a/arch/sparc/include/asm/cache.h +++ b/arch/sparc/include/asm/cache.h @@ -8,7 +8,7 @@ #ifndef _SPARC_CACHE_H #define _SPARC_CACHE_H -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) #define L1_CACHE_SHIFT 5 #define L1_CACHE_BYTES 32 diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h index 4489a27d527a..e3ea278e3fcf 100644 --- a/arch/xtensa/include/asm/processor.h +++ b/arch/xtensa/include/asm/processor.h @@ -18,7 +18,7 @@ #include <asm/types.h> #include <asm/regs.h> -#define ARCH_SLAB_MINALIGN XTENSA_STACK_ALIGNMENT +#define ARCH_SLAB_MIN_MINALIGN XTENSA_STACK_ALIGNMENT /* * User space process size: 1 GB. diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c index 626898150011..8ff1bf7d1e87 100644 --- a/fs/binfmt_flat.c +++ b/fs/binfmt_flat.c @@ -64,7 +64,10 @@ * Here we can be a bit looser than the data sections since this * needs to only meet arch ABI requirements. */ -#define FLAT_STACK_ALIGN max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN) +static size_t flat_stack_align(void) +{ + return max_t(unsigned long, sizeof(void *), arch_slab_minalign()); +} #define RELOC_FAILED 0xff00ff01 /* Relocation incorrect somewhere */ #define UNLOADED_LIB 0x7ff000ff /* Placeholder for unused library */ @@ -148,7 +151,7 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start sp -= 2; /* argvp + envp */ sp -= 1; /* &argc */ - current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN; + current->mm->start_stack = (unsigned long)sp & -flat_stack_align(); sp = (unsigned long __user *)current->mm->start_stack; if (put_user(bprm->argc, sp++)) @@ -966,7 +969,7 @@ static int load_flat_binary(struct linux_binprm *bprm) #endif stack_len += (bprm->argc + 1) * sizeof(char *); /* the argv array */ stack_len += (bprm->envc + 1) * sizeof(char *); /* the envp array */ - stack_len = ALIGN(stack_len, FLAT_STACK_ALIGN); + stack_len = ALIGN(stack_len, flat_stack_align()); res = load_flat_file(bprm, &libinfo, 0, &stack_len); if (res < 0) diff --git a/include/crypto/hash.h b/include/crypto/hash.h index f140e4643949..442c290f458c 100644 --- a/include/crypto/hash.h +++ b/include/crypto/hash.h @@ -149,7 +149,7 @@ struct ahash_alg { struct shash_desc { struct crypto_shash *tfm; - void *__ctx[] __aligned(ARCH_SLAB_MINALIGN); + void *__ctx[] __aligned(ARCH_SLAB_MIN_MINALIGN); }; #define HASH_MAX_DIGESTSIZE 64 diff --git a/include/linux/slab.h b/include/linux/slab.h index 373b3ef99f4e..80e517593372 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object); #endif /* - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment. + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment. * Intended for arches that get misalignment faults even for 64 bit integer * aligned buffers. */ -#ifndef ARCH_SLAB_MINALIGN -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long) +#ifndef ARCH_SLAB_MIN_MINALIGN +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long) +#endif + +/* + * Arches can define this function if they want to decide the minimum slab + * alignment at runtime. The value returned by the function must be + * >= ARCH_SLAB_MIN_MINALIGN. + */ +#ifndef arch_slab_minalign +static inline size_t arch_slab_minalign(void) +{ + return ARCH_SLAB_MIN_MINALIGN; +} #endif /* * kmalloc and friends return ARCH_KMALLOC_MINALIGN aligned - * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MINALIGN + * pointers. kmem_cache_alloc and friends return ARCH_SLAB_MIN_MINALIGN * aligned pointers. */ #define __assume_kmalloc_alignment __assume_aligned(ARCH_KMALLOC_MINALIGN) -#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MINALIGN) +#define __assume_slab_alignment __assume_aligned(ARCH_SLAB_MIN_MINALIGN) #define __assume_page_alignment __assume_aligned(PAGE_SIZE) /* diff --git a/mm/slab.c b/mm/slab.c index 0edb474edef1..97b756976c8b 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3009,10 +3009,9 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep, objp += obj_offset(cachep); if (cachep->ctor && cachep->flags & SLAB_POISON) cachep->ctor(objp); - if (ARCH_SLAB_MINALIGN && - ((unsigned long)objp & (ARCH_SLAB_MINALIGN-1))) { - pr_err("0x%px: not aligned to ARCH_SLAB_MINALIGN=%d\n", - objp, (int)ARCH_SLAB_MINALIGN); + if ((unsigned long)objp & (arch_slab_minalign() - 1)) { + pr_err("0x%px: not aligned to arch_slab_minalign()=%d\n", objp, + (int)arch_slab_minalign()); } return objp; } diff --git a/mm/slab_common.c b/mm/slab_common.c index 2b3206a2c3b5..33cc49810a54 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -154,8 +154,7 @@ static unsigned int calculate_alignment(slab_flags_t flags, align = max(align, ralign); } - if (align < ARCH_SLAB_MINALIGN) - align = ARCH_SLAB_MINALIGN; + align = max_t(size_t, align, arch_slab_minalign()); return ALIGN(align, sizeof(void *)); } diff --git a/mm/slob.c b/mm/slob.c index 40ea6e2d4ccd..3bd2669bd690 100644 --- a/mm/slob.c +++ b/mm/slob.c @@ -478,7 +478,7 @@ static __always_inline void * __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller) { unsigned int *m; - int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); + int minalign = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign()); void *ret; gfp &= gfp_allowed_mask; @@ -555,7 +555,7 @@ void kfree(const void *block) sp = virt_to_folio(block); if (folio_test_slab(sp)) { - int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); + int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign()); unsigned int *m = (unsigned int *)(block - align); slob_free(m, *m + align); } else { @@ -584,7 +584,7 @@ size_t __ksize(const void *block) if (unlikely(!folio_test_slab(folio))) return folio_size(folio); - align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); + align = max_t(size_t, ARCH_KMALLOC_MINALIGN, arch_slab_minalign()); m = (unsigned int *)(block - align); return SLOB_UNITS(*m) * SLOB_UNIT; }
When CONFIG_KASAN_HW_TAGS is enabled we currently increase the minimum slab alignment to 16. This happens even if MTE is not supported in hardware or disabled via kasan=off, which creates an unnecessary memory overhead in those cases. Eliminate this overhead by making the minimum slab alignment a runtime property and only aligning to 16 if KASAN is enabled at runtime. On a DragonBoard 845c (non-MTE hardware) with a kernel built with CONFIG_KASAN_HW_TAGS, waiting for quiescence after a full Android boot I see the following Slab measurements in /proc/meminfo (median of 3 reboots): Before: 169020 kB After: 167304 kB Link: https://linux-review.googlesource.com/id/I752e725179b43b144153f4b6f584ceb646473ead Signed-off-by: Peter Collingbourne <pcc@google.com> --- arch/arc/include/asm/cache.h | 4 ++-- arch/arm/include/asm/cache.h | 2 +- arch/arm64/include/asm/cache.h | 19 +++++++++++++------ arch/microblaze/include/asm/page.h | 2 +- arch/riscv/include/asm/cache.h | 2 +- arch/sparc/include/asm/cache.h | 2 +- arch/xtensa/include/asm/processor.h | 2 +- fs/binfmt_flat.c | 9 ++++++--- include/crypto/hash.h | 2 +- include/linux/slab.h | 22 +++++++++++++++++----- mm/slab.c | 7 +++---- mm/slab_common.c | 3 +-- mm/slob.c | 6 +++--- 13 files changed, 51 insertions(+), 31 deletions(-)