From 891121e6c02c6242487aa4ea1d5c75b7ecdc45ee Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Fri, 9 Oct 2015 08:32:21 +0530 Subject: powerpc/mm: Differentiate between hugetlb and THP during page walk We need to properly identify whether a hugepage is an explicit or a transparent hugepage in follow_huge_addr(). We used to depend on hugepage shift argument to do that. But in some case that can result in wrong results. For ex: On finding a transparent hugepage we set hugepage shift to PMD_SHIFT. But we can end up clearing the thp pte, via pmdp_huge_get_and_clear. We do prevent reusing the pfn page via the usage of kick_all_cpus_sync(). But that happens after we updated the pte to 0. Hence in follow_huge_addr() we can find hugepage shift set, but transparent huge page check fail for a thp pte. NOTE: We fixed a variant of this race against thp split in commit 691e95fd7396905a38d98919e9c150dbc3ea21a3 ("powerpc/mm/thp: Make page table walk safe against thp split/collapse") Without this patch, we may hit the BUG_ON(flags & FOLL_GET) in follow_page_mask occasionally. In the long term, we may want to switch ppc64 64k page size config to enable CONFIG_ARCH_WANT_GENERAL_HUGETLB Reported-by: David Gibson Signed-off-by: Aneesh Kumar K.V Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/pgtable-ppc64.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'arch/powerpc/include/asm/pgtable-ppc64.h') diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h index fa1dfb7f7b48..3245f2d96d4f 100644 --- a/arch/powerpc/include/asm/pgtable-ppc64.h +++ b/arch/powerpc/include/asm/pgtable-ppc64.h @@ -437,9 +437,9 @@ static inline char *get_hpte_slot_array(pmd_t *pmdp) } +#ifdef CONFIG_TRANSPARENT_HUGEPAGE extern void hpte_do_hugepage_flush(struct mm_struct *mm, unsigned long addr, pmd_t *pmdp, unsigned long old_pmd); -#ifdef CONFIG_TRANSPARENT_HUGEPAGE extern pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot); extern pmd_t mk_pmd(struct page *page, pgprot_t pgprot); extern pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot); @@ -479,6 +479,14 @@ static inline int pmd_trans_splitting(pmd_t pmd) } extern int has_transparent_hugepage(void); +#else +static inline void hpte_do_hugepage_flush(struct mm_struct *mm, + unsigned long addr, pmd_t *pmdp, + unsigned long old_pmd) +{ + + WARN(1, "%s called with THP disabled\n", __func__); +} #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ static inline int pmd_large(pmd_t pmd) -- cgit v1.2.3