On 2025/2/27 00:23, Brian Geffon wrote:
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.
Cc: stable@vger.kernel.org Cc: Hugh Dickins hughd@google.com Fixes: 43e027e41423 ("mm: memory: extend finish_fault() to support large folio") Suggested-by: Baolin Wang baolin.wang@linux.alibaba.com Reported-by: Marek Maslanka mmaslanka@google.com Signed-off-by: Brian Geffon bgeffon@google.com
mm/memory.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c index b4d3d4893267..b6c467fdbfa4 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5183,7 +5183,11 @@ 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) @@ -5222,7 +5226,8 @@ 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)) {
Nit: can you align the code? Otherwise look good to me.
nr_pages = 1;} else if (nr_pages > 1) { pgoff_t idx = folio_page_idx(folio, page); @@ -5258,9 +5263,9 @@ 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);