[PATCH] mm: always fallback to PTE mappings for shared write faults

[Pedro Falcato]

Signed-off-by: Pedro Falcato <pfalcato@xxxxxxx>
---
 mm/memory.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index b4be57b590ce..d37f8a0f8355 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5778,6 +5778,16 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 		 */
 		needs_fallback = !shmem_mapping(mapping) &&
 			file_end < folio_next_index(folio);
+
+		if (vma->vm_flags & VM_SHARED && vma->vm_ops->page_mkwrite &&
+		    vmf->flags & FAULT_FLAG_WRITE) {
+			/*
+			 * Filesystems that want write notification want as
+			 * much granular of a mapping as possible. Don't
+			 * install writable THPs for those.
+			 */
+			needs_fallback = true;
+		}
 	}
 
 	if (pmd_none(*vmf->pmd)) {
-- 
2.55.0


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