6.12-stable review patch. If anyone has any objections, please let me know.
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From: Brian Geffon bgeffon@google.com
commit 34b82f33cf3f03bc39e9a205a913d790e1520ade upstream.
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: 43e027e41423 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/memory.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
--- a/mm/memory.c +++ b/mm/memory.c @@ -5079,7 +5079,11 @@ 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) @@ -5118,7 +5122,8 @@ 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); @@ -5154,9 +5159,9 @@ 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);