On 5/7/20 8:07 PM, Anshuman Khandual wrote: > Platform specific huge_ptep_get() is required only when fetching the huge > PTE involves more than just dereferencing the page table pointer. This is > not the case on arm64 platform. Hence huge_ptep_pte() can be dropped along > with it's __HAVE_ARCH_HUGE_PTEP_GET subscription. Before that, it updates > the generic huge_ptep_get() with READ_ONCE() which will prevent known page > table issues with THP on arm64. > > https://lore.kernel.org/r/1506527369-19535-1-git-send-email-will.dea...@arm.com/ > > Cc: Catalin Marinas <catalin.mari...@arm.com> > Cc: Will Deacon <w...@kernel.org> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: linux-arm-ker...@lists.infradead.org > Cc: linux...@kvack.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual <anshuman.khand...@arm.com> > --- > arch/arm64/include/asm/hugetlb.h | 6 ------ > include/asm-generic/hugetlb.h | 2 +- > 2 files changed, 1 insertion(+), 7 deletions(-) > > diff --git a/arch/arm64/include/asm/hugetlb.h > b/arch/arm64/include/asm/hugetlb.h > index 2eb6c234d594..b88878ddc88b 100644 > --- a/arch/arm64/include/asm/hugetlb.h > +++ b/arch/arm64/include/asm/hugetlb.h > @@ -17,12 +17,6 @@ > extern bool arch_hugetlb_migration_supported(struct hstate *h); > #endif > > -#define __HAVE_ARCH_HUGE_PTEP_GET > -static inline pte_t huge_ptep_get(pte_t *ptep) > -{ > - return READ_ONCE(*ptep); > -} > - > static inline int is_hugepage_only_range(struct mm_struct *mm, > unsigned long addr, unsigned long len) > { > diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h > index 822f433ac95c..40f85decc2ee 100644 > --- a/include/asm-generic/hugetlb.h > +++ b/include/asm-generic/hugetlb.h > @@ -122,7 +122,7 @@ static inline int huge_ptep_set_access_flags(struct > vm_area_struct *vma, > #ifndef __HAVE_ARCH_HUGE_PTEP_GET > static inline pte_t huge_ptep_get(pte_t *ptep) > { > - return *ptep; > + return READ_ONCE(*ptep); > } > #endif
I know you made this change in response to Will's comment. And, since changes were made to consistently use READ_ONCE in arm64 code, it makes sense for that architecture. However, with this change to generic code, you introduce READ_ONCE to other architectures where it was not used before. Could this possibly introduce inconsistencies in their use of READ_ONCE? To be honest, I am not very good at identifying any possible issues this could cause. However, it does seem possible. Will was nervous about dropping this from arm64. I'm just a little nervous about adding it to other architectures. -- Mike Kravetz
