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@xxxxxxxxxxxxxxx
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Fixes: 43e027e41423 ("mm: memory: extend finish_fault() to support large folio")
Suggested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Reported-by: Marek Maslanka <mmaslanka@xxxxxxxxxx>
Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
---
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);
