From: Hugh Dickins hughd@google.com
commit 3b77e8c8cde581dadab9a0f1543a347e24315f11 upstream.
Most callers of is_huge_zero_pmd() supply a pmd already verified present; but a few (notably zap_huge_pmd()) do not - it might be a pmd migration entry, in which the pfn is encoded differently from a present pmd: which might pass the is_huge_zero_pmd() test (though not on x86, since L1TF forced us to protect against that); or perhaps even crash in pmd_page() applied to a swap-like entry.
Make it safe by adding pmd_present() check into is_huge_zero_pmd() itself; and make it quicker by saving huge_zero_pfn, so that is_huge_zero_pmd() will not need to do that pmd_page() lookup each time.
__split_huge_pmd_locked() checked pmd_trans_huge() before: that worked, but is unnecessary now that is_huge_zero_pmd() checks present.
Link: https://lkml.kernel.org/r/21ea9ca-a1f5-8b90-5e88-95fb1c49bbfa@google.com Fixes: e71769ae5260 ("mm: enable thp migration for shmem thp") Signed-off-by: Hugh Dickins hughd@google.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reviewed-by: Yang Shi shy828301@gmail.com Cc: Alistair Popple apopple@nvidia.com Cc: Jan Kara jack@suse.cz Cc: Jue Wang juew@google.com Cc: "Matthew Wilcox (Oracle)" willy@infradead.org Cc: Miaohe Lin linmiaohe@huawei.com Cc: Minchan Kim minchan@kernel.org Cc: Naoya Horiguchi naoya.horiguchi@nec.com Cc: Oscar Salvador osalvador@suse.de Cc: Peter Xu peterx@redhat.com Cc: Ralph Campbell rcampbell@nvidia.com Cc: Shakeel Butt shakeelb@google.com Cc: Wang Yugui wangyugui@e16-tech.com Cc: Zi Yan ziy@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/huge_mm.h | 8 +++++++- mm/huge_memory.c | 5 ++++- 2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index d8b86fd39113..d2dbe462efee 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -259,6 +259,7 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, extern vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t orig_pmd);
extern struct page *huge_zero_page; +extern unsigned long huge_zero_pfn;
static inline bool is_huge_zero_page(struct page *page) { @@ -267,7 +268,7 @@ static inline bool is_huge_zero_page(struct page *page)
static inline bool is_huge_zero_pmd(pmd_t pmd) { - return is_huge_zero_page(pmd_page(pmd)); + return READ_ONCE(huge_zero_pfn) == pmd_pfn(pmd) && pmd_present(pmd); }
static inline bool is_huge_zero_pud(pud_t pud) @@ -398,6 +399,11 @@ static inline bool is_huge_zero_page(struct page *page) return false; }
+static inline bool is_huge_zero_pmd(pmd_t pmd) +{ + return false; +} + static inline bool is_huge_zero_pud(pud_t pud) { return false; diff --git a/mm/huge_memory.c b/mm/huge_memory.c index e74c5a505e2b..47d95048f31e 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -61,6 +61,7 @@ static struct shrinker deferred_split_shrinker;
static atomic_t huge_zero_refcount; struct page *huge_zero_page __read_mostly; +unsigned long huge_zero_pfn __read_mostly = ~0UL;
bool transparent_hugepage_enabled(struct vm_area_struct *vma) { @@ -97,6 +98,7 @@ static struct page *get_huge_zero_page(void) __free_pages(zero_page, compound_order(zero_page)); goto retry; } + WRITE_ONCE(huge_zero_pfn, page_to_pfn(zero_page));
/* We take additional reference here. It will be put back by shrinker */ atomic_set(&huge_zero_refcount, 2); @@ -146,6 +148,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink, if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) { struct page *zero_page = xchg(&huge_zero_page, NULL); BUG_ON(zero_page == NULL); + WRITE_ONCE(huge_zero_pfn, ~0UL); __free_pages(zero_page, compound_order(zero_page)); return HPAGE_PMD_NR; } @@ -2182,7 +2185,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, return; }
- if (pmd_trans_huge(*pmd) && is_huge_zero_pmd(*pmd)) { + if (is_huge_zero_pmd(*pmd)) { /* * FIXME: Do we want to invalidate secondary mmu by calling * mmu_notifier_invalidate_range() see comments below inside