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mm: fix finish_fault() handling for large folios

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When handling faults for anon shmem finish_fault() will attempt to install
ptes for the entire folio.  Unfortunately if it encounters a single
non-pte_none entry in that range it will bail, even if the pte that
triggered the fault is still pte_none.  When this situation happens the
fault will be retried endlessly never making forward progress.

This patch fixes this behavior and if it detects that a pte in the range
is not pte_none it will fall back to setting a single pte.

[bgeffon@google.com: tweak whitespace]
  Link: https://lkml.kernel.org/r/20250227133236.1296853-1-bgeffon@google.com
Link: https://lkml.kernel.org/r/20250226162341.915535-1-bgeffon@google.com
Fixes: 43e027e414 ("mm: memory: extend finish_fault() to support large folio")
Signed-off-by: Brian Geffon <bgeffon@google.com>
Suggested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reported-by: Marek Maslanka <mmaslanka@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickens <hughd@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Brian Geffon 2025-02-26 11:23:41 -05:00 committed by Andrew Morton
parent 3685024edd
commit 34b82f33cf
1 changed files with 10 additions and 5 deletions
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15
mm/memory.c
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@ -5185,7 +5185,11 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
bool is_cow = (vmf->flags & FAULT_FLAG_WRITE) &&
!(vma->vm_flags & VM_SHARED);
int type, nr_pages;
unsigned long addr = vmf->address;
unsigned long addr;
bool needs_fallback = false;
fallback:
addr = vmf->address;
/* Did we COW the page? */
if (is_cow)
@ -5224,7 +5228,8 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
* approach also applies to non-anonymous-shmem faults to avoid
* inflating the RSS of the process.
*/
if (!vma_is_anon_shmem(vma) || unlikely(userfaultfd_armed(vma))) {
if (!vma_is_anon_shmem(vma) || unlikely(userfaultfd_armed(vma)) ||
unlikely(needs_fallback)) {
nr_pages = 1;
} else if (nr_pages > 1) {
pgoff_t idx = folio_page_idx(folio, page);
@ -5260,9 +5265,9 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
ret = VM_FAULT_NOPAGE;
goto unlock;
} else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
ret = VM_FAULT_NOPAGE;
goto unlock;
needs_fallback = true;
pte_unmap_unlock(vmf->pte, vmf->ptl);
goto fallback;
}
folio_ref_add(folio, nr_pages - 1);