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Wed, 04 Jan 2023 15:19:23 -0800 (PST) Date: Wed, 4 Jan 2023 23:19:10 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.39.0.314.g84b9a713c41-goog Message-ID: <20230104231910.1464197-1-jthoughton@google.com> Subject: [PATCH v2] hugetlb: unshare some PMDs when splitting VMAs From: James Houghton To: Mike Kravetz , Muchun Song , Peter Xu Cc: Axel Rasmussen , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, James Houghton Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 995AEC0008 X-Rspam-User: X-Stat-Signature: awod99t7wczyrw79cmdha8y9i4zzaf7j X-HE-Tag: 1672874364-836980 X-HE-Meta: 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 VT6IdmJ+ 6NfDwflUSN4MvsP6j96dd8g8R0mEqEwPCKII1H5X9h7JLh4Ap9AkYV6mcTJodNAmw1ORqbxibx7QYgpCc7m/ee4D7/wFPWzQD/XjyDPGmH89/ssDxkjpGuzNIQKeCoq6mPDsQwiVQSxBwx/43PbmaGmc1P2mPzFY4M5B1Pj3KRWX7ue8M6ultsF+/BRDarp04Kalkya7Z8LhbYKNpQbdiTV6SIeQA0vbxQCU0gB6CGC/s6FaZP1eeMOPS3UFFeGHvR/lRgeNhLql0wuOdxZps7gsh2i/th3vYxgLsG8dCaSvGHZV6oAuJCgHMuSBpaE4ME5B+sXHBDdg/+FaU0DYG97BVYGGvROtzzov8B0SHLmWF+oEZl/FP1lCISvvYy2hFD6GlVCD2meqAn48= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: PMD sharing can only be done in PUD_SIZE-aligned pieces of VMAs; however, it is possible that HugeTLB VMAs are split without unsharing the PMDs first. Without this fix, it is possible to hit the uffd-wp-related WARN_ON_ONCE in hugetlb_change_protection [1]. The key there is that hugetlb_unshare_all_pmds will not attempt to unshare PMDs in non-PUD_SIZE-aligned sections of the VMA. It might seem ideal to unshare in hugetlb_vm_op_open, but we need to unshare in both the new and old VMAs, so unsharing in hugetlb_vm_op_split seems natural. [1]: https://lore.kernel.org/linux-mm/CADrL8HVeOkj0QH5VZZbRzybNE8CG-tEGFshnA+bG9nMgcWtBSg@mail.gmail.com/ Fixes: 6dfeaff93be1 ("hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp") Signed-off-by: James Houghton --- mm/hugetlb.c | 44 +++++++++++++++++++++++++++++++++++--------- 1 file changed, 35 insertions(+), 9 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index b39b74e0591a..b6976da0fa4d 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -94,6 +94,8 @@ static int hugetlb_acct_memory(struct hstate *h, long delta); static void hugetlb_vma_lock_free(struct vm_area_struct *vma); static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma); static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma); +static void hugetlb_unshare_pmds(struct vm_area_struct *vma, + unsigned long start, unsigned long end); static inline bool subpool_is_free(struct hugepage_subpool *spool) { @@ -4828,6 +4830,25 @@ static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr) { if (addr & ~(huge_page_mask(hstate_vma(vma)))) return -EINVAL; + + /* + * PMD sharing is only possible for PUD_SIZE-aligned address ranges + * in HugeTLB VMAs. If we will lose PUD_SIZE alignment due to this + * split, unshare PMDs in the PUD_SIZE interval surrounding addr now. + */ + if (addr & ~PUD_MASK) { + /* + * hugetlb_vm_op_split is called right before we attempt to + * split the VMA. We will need to unshare PMDs in the old and + * new VMAs, so let's unshare before we split. + */ + unsigned long floor = addr & PUD_MASK; + unsigned long ceil = floor + PUD_SIZE; + + if (floor >= vma->vm_start && ceil <= vma->vm_end) + hugetlb_unshare_pmds(vma, floor, ceil); + } + return 0; } @@ -7313,26 +7334,21 @@ void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio, int re } } -/* - * This function will unconditionally remove all the shared pmd pgtable entries - * within the specific vma for a hugetlbfs memory range. - */ -void hugetlb_unshare_all_pmds(struct vm_area_struct *vma) +static void hugetlb_unshare_pmds(struct vm_area_struct *vma, + unsigned long start, + unsigned long end) { struct hstate *h = hstate_vma(vma); unsigned long sz = huge_page_size(h); struct mm_struct *mm = vma->vm_mm; struct mmu_notifier_range range; - unsigned long address, start, end; + unsigned long address; spinlock_t *ptl; pte_t *ptep; if (!(vma->vm_flags & VM_MAYSHARE)) return; - start = ALIGN(vma->vm_start, PUD_SIZE); - end = ALIGN_DOWN(vma->vm_end, PUD_SIZE); - if (start >= end) return; @@ -7364,6 +7380,16 @@ void hugetlb_unshare_all_pmds(struct vm_area_struct *vma) mmu_notifier_invalidate_range_end(&range); } +/* + * This function will unconditionally remove all the shared pmd pgtable entries + * within the specific vma for a hugetlbfs memory range. + */ +void hugetlb_unshare_all_pmds(struct vm_area_struct *vma) +{ + hugetlb_unshare_pmds(vma, ALIGN(vma->vm_start, PUD_SIZE), + ALIGN_DOWN(vma->vm_end, PUD_SIZE)); +} + #ifdef CONFIG_CMA static bool cma_reserve_called __initdata; -- 2.39.0.314.g84b9a713c41-goog