+ mm-damon-validate-if-the-pmd-entry-is-present-before-accessing.patch added to mm-unstable branch

* + mm-damon-validate-if-the-pmd-entry-is-present-before-accessing.patch added to mm-unstable branch
@ 2022-08-20 21:20 Andrew Morton
  0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2022-08-20 21:20 UTC (permalink / raw)
  To: mm-commits, songmuchun, sj, mike.kravetz, baolin.wang, akpm


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@linux.alibaba.com>
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@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@linux.alibaba.com 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


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