+ mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch added to -mm tree

+ mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm: rmap: explicitly reset vma->anon_vma in unlink_anon_vmas()
has been added to the -mm tree.  Its filename is
     mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch

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------------------------------------------------------
From: Li Xinhai <lixinhai.lxh@gmail.com>
Subject: mm: rmap: explicitly reset vma->anon_vma in unlink_anon_vmas()

In case the vma will continue to be used after unlink its relevant
anon_vma, we need to reset the vma->anon_vma pointer to NULL.  So, later
when fault happen within this vma again, a new anon_vma will be prepared.

By this way, the vma will only be checked for reverse mapping of pages
which been fault in after the unlink_anon_vmas call.

Currently, the mremap with MREMAP_DONTUNMAP scenario will continue use the
vma after moved its page table entries to a new vma.  For other scenarios,
the vma itself will be freed after call unlink_anon_vmas.

Link: https://lkml.kernel.org/r/20210119075126.3513154-1-lixinhai.lxh@gmail.com
Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/rmap.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/rmap.c~mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas
+++ a/mm/rmap.c
@@ -413,8 +413,15 @@ void unlink_anon_vmas(struct vm_area_str
 		list_del(&avc->same_vma);
 		anon_vma_chain_free(avc);
 	}
-	if (vma->anon_vma)
+	if (vma->anon_vma) {
 		vma->anon_vma->degree--;
+
+		/*
+		 * vma would still be needed after unlink, and anon_vma will be prepared
+		 * when handle fault.
+		 */
+		vma->anon_vma = NULL;
+	}
 	unlock_anon_vma_root(root);
 
 	/*
_

Patches currently in -mm which might be from lixinhai.lxh@gmail.com are

mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch
mm-mremap-unlink-anon_vmas-when-mremap-with-mremap_dontunmap-success.patch
mm-hugetlbc-fix-unnecessary-address-expansion-of-pmd-sharing.patch