From: James Houghton <jthoughton@xxxxxxxxxx> [ Upstream commit b30c14cd61025eeea2f2e8569606cd167ba9ad2d ] 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@xxxxxxxxxxxxxx/ Link: https://lkml.kernel.org/r/20230104231910.1464197-1-jthoughton@xxxxxxxxxx Fixes: 6dfeaff93be1 ("hugetlb/userfaultfd: unshare all pmds for hugetlbfs when register wp") Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Peter Xu <peterx@xxxxxxxxxx> Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- mm/hugetlb.c | 44 +++++++++++++++++++++++++++++++++++--------- 1 file changed, 35 insertions(+), 9 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index e7bd42f23667..8599f16d4aa4 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -82,6 +82,8 @@ struct mutex *hugetlb_fault_mutex_table ____cacheline_aligned_in_smp; /* Forward declaration */ static int hugetlb_acct_memory(struct hstate *h, long delta); +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) { @@ -4164,6 +4166,25 @@ 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; } @@ -6349,26 +6370,21 @@ void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason) } } -/* - * 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; @@ -6400,6 +6416,16 @@ 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
