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.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'arch/powerpc/include/asm/pgtable.h') diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h index 0717693c8428..b64b4212b71f 100644 --- a/arch/powerpc/include/asm/pgtable.h +++ b/arch/powerpc/include/asm/pgtable.h @@ -259,15 +259,15 @@ extern int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, #define has_transparent_hugepage() 0 #endif pte_t *__find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, - unsigned *shift); + bool *is_thp, unsigned *shift); static inline pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, - unsigned *shift) + bool *is_thp, unsigned *shift) { if (!arch_irqs_disabled()) { pr_info("%s called with irq enabled\n", __func__); dump_stack(); } - return __find_linux_pte_or_hugepte(pgdir, ea, shift); + return __find_linux_pte_or_hugepte(pgdir, ea, is_thp, shift); } #endif /* __ASSEMBLY__ */ -- cgit v1.2.3