| Message ID | 20210115120043.50023-5-vincenzo.frascino@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: ARMv8.5-A: MTE: Add async mode support | expand |
On Fri, Jan 15, 2021 at 12:00:43PM +0000, Vincenzo Frascino wrote: > mte_assign_mem_tag_range() is called on production KASAN HW hot > paths. It makes sense to optimize it in an attempt to reduce the > overhead. > > Optimize mte_assign_mem_tag_range() based on the indications provided at > [1]. ... what exactly is the optimization? I /think/ you're just trying to have it inlined, but you should mention that explicitly. > > [1] https://lore.kernel.org/r/CAAeHK+wCO+J7D1_T89DG+jJrPLk3X9RsGFKxJGd0ZcUFjQT-9Q@mail.gmail.com/ > > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> > --- > arch/arm64/include/asm/mte.h | 26 +++++++++++++++++++++++++- > arch/arm64/lib/mte.S | 15 --------------- > 2 files changed, 25 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h > index 1a715963d909..9730f2b07b79 100644 > --- a/arch/arm64/include/asm/mte.h > +++ b/arch/arm64/include/asm/mte.h > @@ -49,7 +49,31 @@ long get_mte_ctrl(struct task_struct *task); > int mte_ptrace_copy_tags(struct task_struct *child, long request, > unsigned long addr, unsigned long data); > > -void mte_assign_mem_tag_range(void *addr, size_t size); > +static inline void mte_assign_mem_tag_range(void *addr, size_t size) > +{ > + u64 _addr = (u64)addr; > + u64 _end = _addr + size; > + > + /* > + * This function must be invoked from an MTE enabled context. > + * > + * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and > + * size must be non-zero and MTE_GRANULE_SIZE aligned. > + */ > + do { > + /* > + * 'asm volatile' is required to prevent the compiler to move > + * the statement outside of the loop. > + */ > + asm volatile(__MTE_PREAMBLE "stg %0, [%0]" > + : > + : "r" (_addr) > + : "memory"); > + > + _addr += MTE_GRANULE_SIZE; > + } while (_addr < _end); Is there any chance that this can be used for the last bytes of the virtual address space? This might need to change to `_addr == _end` if that is possible, otherwise it'll terminate early in that case. > +} What does the code generation look like for this, relative to the assembly version? Thanks, Mark. > + > > #else /* CONFIG_ARM64_MTE */ > > diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S > index 9e1a12e10053..a0a650451510 100644 > --- a/arch/arm64/lib/mte.S > +++ b/arch/arm64/lib/mte.S > @@ -150,18 +150,3 @@ SYM_FUNC_START(mte_restore_page_tags) > ret > SYM_FUNC_END(mte_restore_page_tags) > > -/* > - * Assign allocation tags for a region of memory based on the pointer tag > - * x0 - source pointer > - * x1 - size > - * > - * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and > - * size must be non-zero and MTE_GRANULE_SIZE aligned. > - */ > -SYM_FUNC_START(mte_assign_mem_tag_range) > -1: stg x0, [x0] > - add x0, x0, #MTE_GRANULE_SIZE > - subs x1, x1, #MTE_GRANULE_SIZE > - b.gt 1b > - ret > -SYM_FUNC_END(mte_assign_mem_tag_range) > -- > 2.30.0 >
Hi Mark, On 1/15/21 3:45 PM, Mark Rutland wrote: > On Fri, Jan 15, 2021 at 12:00:43PM +0000, Vincenzo Frascino wrote: >> mte_assign_mem_tag_range() is called on production KASAN HW hot >> paths. It makes sense to optimize it in an attempt to reduce the >> overhead. >> >> Optimize mte_assign_mem_tag_range() based on the indications provided at >> [1]. > > ... what exactly is the optimization? > > I /think/ you're just trying to have it inlined, but you should mention > that explicitly. > Good point, I will change it in the next version. I used "Optimize" as a continuation of the topic in the previous thread but you are right it is not immediately obvious. >> >> [1] https://lore.kernel.org/r/CAAeHK+wCO+J7D1_T89DG+jJrPLk3X9RsGFKxJGd0ZcUFjQT-9Q@mail.gmail.com/ >> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> >> --- >> arch/arm64/include/asm/mte.h | 26 +++++++++++++++++++++++++- >> arch/arm64/lib/mte.S | 15 --------------- >> 2 files changed, 25 insertions(+), 16 deletions(-) >> >> diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h >> index 1a715963d909..9730f2b07b79 100644 >> --- a/arch/arm64/include/asm/mte.h >> +++ b/arch/arm64/include/asm/mte.h >> @@ -49,7 +49,31 @@ long get_mte_ctrl(struct task_struct *task); >> int mte_ptrace_copy_tags(struct task_struct *child, long request, >> unsigned long addr, unsigned long data); >> >> -void mte_assign_mem_tag_range(void *addr, size_t size); >> +static inline void mte_assign_mem_tag_range(void *addr, size_t size) >> +{ >> + u64 _addr = (u64)addr; >> + u64 _end = _addr + size; >> + >> + /* >> + * This function must be invoked from an MTE enabled context. >> + * >> + * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and >> + * size must be non-zero and MTE_GRANULE_SIZE aligned. >> + */ >> + do { >> + /* >> + * 'asm volatile' is required to prevent the compiler to move >> + * the statement outside of the loop. >> + */ >> + asm volatile(__MTE_PREAMBLE "stg %0, [%0]" >> + : >> + : "r" (_addr) >> + : "memory"); >> + >> + _addr += MTE_GRANULE_SIZE; >> + } while (_addr < _end); > > Is there any chance that this can be used for the last bytes of the > virtual address space? This might need to change to `_addr == _end` if > that is possible, otherwise it'll terminate early in that case. > Theoretically it is a possibility. I will change the condition and add a note for that. >> +} > > What does the code generation look like for this, relative to the > assembly version? > The assembly looks like this: 390: 8b000022 add x2, x1, x0 394: aa0003e1 mov x1, x0 398: d9200821 stg x1, [x1] 39c: 91004021 add x1, x1, #0x10 3a0: eb01005f cmp x2, x1 3a4: 54ffffa8 b.hi 398 <mte_set_mem_tag_range+0x48> You can see the handcrafted one below. > Thanks, > Mark. > >> + >> >> #else /* CONFIG_ARM64_MTE */ >> >> diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S >> index 9e1a12e10053..a0a650451510 100644 >> --- a/arch/arm64/lib/mte.S >> +++ b/arch/arm64/lib/mte.S >> @@ -150,18 +150,3 @@ SYM_FUNC_START(mte_restore_page_tags) >> ret >> SYM_FUNC_END(mte_restore_page_tags) >> >> -/* >> - * Assign allocation tags for a region of memory based on the pointer tag >> - * x0 - source pointer >> - * x1 - size >> - * >> - * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and >> - * size must be non-zero and MTE_GRANULE_SIZE aligned. >> - */ >> -SYM_FUNC_START(mte_assign_mem_tag_range) >> -1: stg x0, [x0] >> - add x0, x0, #MTE_GRANULE_SIZE >> - subs x1, x1, #MTE_GRANULE_SIZE >> - b.gt 1b >> - ret >> -SYM_FUNC_END(mte_assign_mem_tag_range) >> -- >> 2.30.0 >>
Hi Mark, On 1/16/21 2:22 PM, Vincenzo Frascino wrote: >> Is there any chance that this can be used for the last bytes of the >> virtual address space? This might need to change to `_addr == _end` if >> that is possible, otherwise it'll terminate early in that case. >> > Theoretically it is a possibility. I will change the condition and add a note > for that. > I was thinking to the end of the virtual address space scenario and I forgot that if I use a condition like `_addr == _end` the tagging operation overflows to the first granule of the next allocation. This disrupts tagging accesses for that memory area hence I think that `_addr < _end` is the way to go.
On Sun, Jan 17, 2021 at 12:27:08PM +0000, Vincenzo Frascino wrote: > Hi Mark, > > On 1/16/21 2:22 PM, Vincenzo Frascino wrote: > >> Is there any chance that this can be used for the last bytes of the > >> virtual address space? This might need to change to `_addr == _end` if > >> that is possible, otherwise it'll terminate early in that case. > >> > > Theoretically it is a possibility. I will change the condition and add a note > > for that. > > > > I was thinking to the end of the virtual address space scenario and I forgot > that if I use a condition like `_addr == _end` the tagging operation overflows > to the first granule of the next allocation. This disrupts tagging accesses for > that memory area hence I think that `_addr < _end` is the way to go. I think it implies `_addr != _end` is necessary. Otherwise, if `addr` is PAGE_SIZE from the end of memory, and `size` is PAGE_SIZE, `_end` will be 0, so using `_addr < _end` will mean the loop will terminate after a single MTE tag granule rather than the whole page. Generally, for some addr/increment/size combination (where all are suitably aligned), you need a pattern like: | do { | thing(addr); | addr += increment; | } while (addr != end); ... or: | for (addr = start; addr != end; addr += increment) { | thing(addr); | } ... to correctly handle working at the very end of the VA space. We do similar for page tables, e.g. when we use pmd_addr_end(). Thanks, Mark.
On 1/18/21 10:41 AM, Mark Rutland wrote: > On Sun, Jan 17, 2021 at 12:27:08PM +0000, Vincenzo Frascino wrote: >> Hi Mark, >> >> On 1/16/21 2:22 PM, Vincenzo Frascino wrote: >>>> Is there any chance that this can be used for the last bytes of the >>>> virtual address space? This might need to change to `_addr == _end` if >>>> that is possible, otherwise it'll terminate early in that case. >>>> >>> Theoretically it is a possibility. I will change the condition and add a note >>> for that. >>> >> >> I was thinking to the end of the virtual address space scenario and I forgot >> that if I use a condition like `_addr == _end` the tagging operation overflows >> to the first granule of the next allocation. This disrupts tagging accesses for >> that memory area hence I think that `_addr < _end` is the way to go. > > I think it implies `_addr != _end` is necessary. Otherwise, if `addr` is > PAGE_SIZE from the end of memory, and `size` is PAGE_SIZE, `_end` will > be 0, so using `_addr < _end` will mean the loop will terminate after a > single MTE tag granule rather than the whole page. > > Generally, for some addr/increment/size combination (where all are > suitably aligned), you need a pattern like: > > | do { > | thing(addr); > | addr += increment; > | } while (addr != end); > > ... or: > > | for (addr = start; addr != end; addr += increment) { > | thing(addr); > | } > > ... to correctly handle working at the very end of the VA space. > > We do similar for page tables, e.g. when we use pmd_addr_end(). > Good point! I agree it wraps around otherwise. I will change it accordingly. Thanks! > Thanks, > Mark. >
diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index 1a715963d909..9730f2b07b79 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -49,7 +49,31 @@ long get_mte_ctrl(struct task_struct *task); int mte_ptrace_copy_tags(struct task_struct *child, long request, unsigned long addr, unsigned long data); -void mte_assign_mem_tag_range(void *addr, size_t size); +static inline void mte_assign_mem_tag_range(void *addr, size_t size) +{ + u64 _addr = (u64)addr; + u64 _end = _addr + size; + + /* + * This function must be invoked from an MTE enabled context. + * + * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and + * size must be non-zero and MTE_GRANULE_SIZE aligned. + */ + do { + /* + * 'asm volatile' is required to prevent the compiler to move + * the statement outside of the loop. + */ + asm volatile(__MTE_PREAMBLE "stg %0, [%0]" + : + : "r" (_addr) + : "memory"); + + _addr += MTE_GRANULE_SIZE; + } while (_addr < _end); +} + #else /* CONFIG_ARM64_MTE */ diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S index 9e1a12e10053..a0a650451510 100644 --- a/arch/arm64/lib/mte.S +++ b/arch/arm64/lib/mte.S @@ -150,18 +150,3 @@ SYM_FUNC_START(mte_restore_page_tags) ret SYM_FUNC_END(mte_restore_page_tags) -/* - * Assign allocation tags for a region of memory based on the pointer tag - * x0 - source pointer - * x1 - size - * - * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and - * size must be non-zero and MTE_GRANULE_SIZE aligned. - */ -SYM_FUNC_START(mte_assign_mem_tag_range) -1: stg x0, [x0] - add x0, x0, #MTE_GRANULE_SIZE - subs x1, x1, #MTE_GRANULE_SIZE - b.gt 1b - ret -SYM_FUNC_END(mte_assign_mem_tag_range)
mte_assign_mem_tag_range() is called on production KASAN HW hot paths. It makes sense to optimize it in an attempt to reduce the overhead. Optimize mte_assign_mem_tag_range() based on the indications provided at [1]. [1] https://lore.kernel.org/r/CAAeHK+wCO+J7D1_T89DG+jJrPLk3X9RsGFKxJGd0ZcUFjQT-9Q@mail.gmail.com/ Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> --- arch/arm64/include/asm/mte.h | 26 +++++++++++++++++++++++++- arch/arm64/lib/mte.S | 15 --------------- 2 files changed, 25 insertions(+), 16 deletions(-)