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mm-fix-finish_fault-handling-for-large-folios.patch removed from -mm tree

merged mm-hotfixes-stable Andrew Morton 1 participant 1 message Mar 6, 2025 Stable branch

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The quilt patch titled
Subject: mm: fix finish_fault() handling for large folios
has been removed from the -mm tree. Its filename was
mm-fix-finish_fault-handling-for-large-folios.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Brian Geffon <[email protected]>
Subject: mm: fix finish_fault() handling for large folios
Date: Wed, 26 Feb 2025 11:23:41 -0500

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.

[[email protected]: tweak whitespace]
Link https://lkml.kernel.org/r/[email protected] open here
Link https://lkml.kernel.org/r/[email protected] open here
Fixes 43e027e41423 ("mm: memory: extend finish_fault() to support large folio")
Signed-off-by Brian Geffon <[email protected]>
Suggested-by Baolin Wang <[email protected]>
Reported-by Marek Maslanka <[email protected]>
Cc Hugh Dickins <[email protected]>
Cc David Hildenbrand <[email protected]>
Cc Hugh Dickens <[email protected]>
Cc Kefeng Wang <[email protected]>
Cc Matthew Wilcow (Oracle) <[email protected]>
Cc Suren Baghdasaryan <[email protected]>
Cc Zi Yan <[email protected]>
Cc <[email protected]>
Signed-off-by Andrew Morton <[email protected]>

---

 mm/memory.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)
mm/memory.c renamed from mm/memory.c~mm-fix-finish_fault-handling-for-large-folios +10 -5
@@ -5185,7 +5185,11 @@ vm_fault_t finish_fault(struct vm_fault
 	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
 	 * 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
 		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);

_

Patches currently in -mm which might be from [email protected] are