The patch titled
Subject: mm/damon: validate if the pmd entry is present before accessing
has been added to the -mm mm-unstable branch. Its filename is
mm-damon-validate-if-the-pmd-entry-is-present-before-accessing.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-validate-if-the-pmd-entry-is-present-before-accessing.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Subject: mm/damon: validate if the pmd entry is present before accessing
Date: Thu, 18 Aug 2022 15:37:43 +0800
pmd_huge() is used to validate if the pmd entry is mapped by a huge page,
also including the case of non-present (migration or hwpoisoned) pmd entry
on arm64 or x86 architectures. This means that pmd_pfn() can not get the
correct pfn number for a non-present pmd entry, which will cause
damon_get_page() to get an incorrect page struct (also may be NULL by
pfn_to_online_page()), making the access statistics incorrect.
Moreover it does not make sense that we still waste time to get the page
of the non-present entry. Just treat it as not-accessed and skip it,
which maintains consistency with non-present pte level entries.
So add pmd entry present validation to fix the above issues.
Link: https://lkml.kernel.org/r/58b1d1f5fbda7db49ca886d9ef6783e3dcbbbc98.1660805030.git.baolin.wang@xxxxxxxxxxxxxxxxx
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Reviewed-by: SeongJae Park <sj@xxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/damon/vaddr.c | 10 ++++++++++
1 file changed, 10 insertions(+)
--- a/mm/damon/vaddr.c~mm-damon-validate-if-the-pmd-entry-is-present-before-accessing
+++ a/mm/damon/vaddr.c
@@ -304,6 +304,11 @@ static int damon_mkold_pmd_entry(pmd_t *
if (pmd_huge(*pmd)) {
ptl = pmd_lock(walk->mm, pmd);
+ if (!pmd_present(*pmd)) {
+ spin_unlock(ptl);
+ return 0;
+ }
+
if (pmd_huge(*pmd)) {
damon_pmdp_mkold(pmd, walk->mm, addr);
spin_unlock(ptl);
@@ -431,6 +436,11 @@ static int damon_young_pmd_entry(pmd_t *
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
if (pmd_huge(*pmd)) {
ptl = pmd_lock(walk->mm, pmd);
+ if (!pmd_present(*pmd)) {
+ spin_unlock(ptl);
+ return 0;
+ }
+
if (!pmd_huge(*pmd)) {
spin_unlock(ptl);
goto regular_page;
_
Patches currently in -mm which might be from baolin.wang@xxxxxxxxxxxxxxxxx are
mm-migrate-do-not-retry-10-times-for-the-subpages-of-fail-to-migrate-thp.patch
mm-damon-validate-if-the-pmd-entry-is-present-before-accessing.patch
mm-damon-replace-pmd_huge-with-pmd_trans_huge-for-thp.patch
