| Message ID | 1557824407-19092-4-git-send-email-anshuman.khandual@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64/mm: Enable memory hot remove | expand |
On 14.05.19 11:00, Anshuman Khandual wrote: > From: Mark Rutland <mark.rutland@arm.com> > > The arm64 ptdump code can race with concurrent modification of the > kernel page tables. At the time this was added, this was sound as: > > * Modifications to leaf entries could result in stale information being > logged, but would not result in a functional problem. > > * Boot time modifications to non-leaf entries (e.g. freeing of initmem) > were performed when the ptdump code cannot be invoked. > > * At runtime, modifications to non-leaf entries only occurred in the > vmalloc region, and these were strictly additive, as intermediate > entries were never freed. > > However, since commit: > > commit 324420bf91f6 ("arm64: add support for ioremap() block mappings") > > ... it has been possible to create huge mappings in the vmalloc area at > runtime, and as part of this existing intermediate levels of table my be > removed and freed. > > It's possible for the ptdump code to race with this, and continue to > walk tables which have been freed (and potentially poisoned or > reallocated). As a result of this, the ptdump code may dereference bogus > addresses, which could be fatal. > > Since huge-vmap is a TLB and memory optimization, we can disable it when > the runtime ptdump code is in use to avoid this problem. I wonder if there is another way to protect from such a race happening. (IOW, a lock). But as you say, it's a debug feature, so this is an easy fix. Looks good to me (with limited arm64 code insight :) ) > > Fixes: 324420bf91f60582 ("arm64: add support for ioremap() block mappings") > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will.deacon@arm.com> > --- > arch/arm64/mm/mmu.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index ef82312..37a902c 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -955,13 +955,18 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys) > > int __init arch_ioremap_pud_supported(void) > { > - /* only 4k granule supports level 1 block mappings */ > - return IS_ENABLED(CONFIG_ARM64_4K_PAGES); > + /* > + * Only 4k granule supports level 1 block mappings. > + * SW table walks can't handle removal of intermediate entries. > + */ > + return IS_ENABLED(CONFIG_ARM64_4K_PAGES) && > + !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); > } > > int __init arch_ioremap_pmd_supported(void) > { > - return 1; > + /* See arch_ioremap_pud_supported() */ > + return !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); > } > > int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot) >
On Tue, 14 May 2019 at 11:00, Anshuman Khandual <anshuman.khandual@arm.com> wrote: > > From: Mark Rutland <mark.rutland@arm.com> > > The arm64 ptdump code can race with concurrent modification of the > kernel page tables. At the time this was added, this was sound as: > > * Modifications to leaf entries could result in stale information being > logged, but would not result in a functional problem. > > * Boot time modifications to non-leaf entries (e.g. freeing of initmem) > were performed when the ptdump code cannot be invoked. > > * At runtime, modifications to non-leaf entries only occurred in the > vmalloc region, and these were strictly additive, as intermediate > entries were never freed. > > However, since commit: > > commit 324420bf91f6 ("arm64: add support for ioremap() block mappings") > > ... it has been possible to create huge mappings in the vmalloc area at > runtime, and as part of this existing intermediate levels of table my be > removed and freed. > > It's possible for the ptdump code to race with this, and continue to > walk tables which have been freed (and potentially poisoned or > reallocated). As a result of this, the ptdump code may dereference bogus > addresses, which could be fatal. > > Since huge-vmap is a TLB and memory optimization, we can disable it when > the runtime ptdump code is in use to avoid this problem. > The reason I added this originally is so that we don't trigger a warning when unmapping vmappings that use 2 MB block mappings, which happens when we free the kernel's .init segment. The ability to create such mappings is indeed an optimization that the kernel mapping code does not rely on. > Fixes: 324420bf91f60582 ("arm64: add support for ioremap() block mappings") > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will.deacon@arm.com> Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com> > --- > arch/arm64/mm/mmu.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index ef82312..37a902c 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -955,13 +955,18 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys) > > int __init arch_ioremap_pud_supported(void) > { > - /* only 4k granule supports level 1 block mappings */ > - return IS_ENABLED(CONFIG_ARM64_4K_PAGES); > + /* > + * Only 4k granule supports level 1 block mappings. > + * SW table walks can't handle removal of intermediate entries. > + */ > + return IS_ENABLED(CONFIG_ARM64_4K_PAGES) && > + !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); > } > > int __init arch_ioremap_pmd_supported(void) > { > - return 1; > + /* See arch_ioremap_pud_supported() */ > + return !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); > } > > int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot) > -- > 2.7.4 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index ef82312..37a902c 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -955,13 +955,18 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys) int __init arch_ioremap_pud_supported(void) { - /* only 4k granule supports level 1 block mappings */ - return IS_ENABLED(CONFIG_ARM64_4K_PAGES); + /* + * Only 4k granule supports level 1 block mappings. + * SW table walks can't handle removal of intermediate entries. + */ + return IS_ENABLED(CONFIG_ARM64_4K_PAGES) && + !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); } int __init arch_ioremap_pmd_supported(void) { - return 1; + /* See arch_ioremap_pud_supported() */ + return !IS_ENABLED(CONFIG_ARM64_PTDUMP_DEBUGFS); } int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot)