linux-kernel - [PATCH v1 3/4] mm/rmap: fix two comments related to huge_pmd

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20251205213558.2980480-4-david@kernel.org>
Date: Fri,  5 Dec 2025 22:35:57 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: linux-arch@...r.kernel.org,
	linux-mm@...ck.org,
	"David Hildenbrand (Red Hat)" <david@...nel.org>,
	Will Deacon <will@...nel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	Muchun Song <muchun.song@...ux.dev>,
	Oscar Salvador <osalvador@...e.de>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Jann Horn <jannh@...gle.com>,
	Pedro Falcato <pfalcato@...e.de>,
	Rik van Riel <riel@...riel.com>,
	Harry Yoo <harry.yoo@...cle.com>,
	Laurence Oberman <loberman@...hat.com>,
	Prakash Sangappa <prakash.sangappa@...cle.com>,
	Nadav Amit <nadav.amit@...il.com>,
	Liu Shixin <liushixin2@...wei.com>
Subject: [PATCH v1 3/4] mm/rmap: fix two comments related to huge_pmd_unshare()

PMD page table unsharing no longer touches the refcount of a PMD page
table. Also, it is not about dropping the refcount of a "PMD page" but
the "PMD page table".

Let's just simplify by saying that the PMD page table was unmapped,
consequently also unmapping the folio that was mapped into this page.

This code should be deduplicated in the future.

Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count")
Cc: Liu Shixin <liushixin2@...wei.com>
Signed-off-by: David Hildenbrand (Red Hat) <david@...nel.org>
---
 mm/rmap.c | 20 ++++----------------
 1 file changed, 4 insertions(+), 16 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index f955f02d570ed..748f48727a162 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2016,14 +2016,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 					flush_tlb_range(vma,
 						range.start, range.end);
 					/*
-					 * The ref count of the PMD page was
-					 * dropped which is part of the way map
-					 * counting is done for shared PMDs.
-					 * Return 'true' here.  When there is
-					 * no other sharing, huge_pmd_unshare
-					 * returns false and we will unmap the
-					 * actual page and drop map count
-					 * to zero.
+					 * The PMD table was unmapped,
+					 * consequently unmapping the folio.
 					 */
 					goto walk_done;
 				}
@@ -2416,14 +2410,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 						range.start, range.end);
 
 					/*
-					 * The ref count of the PMD page was
-					 * dropped which is part of the way map
-					 * counting is done for shared PMDs.
-					 * Return 'true' here.  When there is
-					 * no other sharing, huge_pmd_unshare
-					 * returns false and we will unmap the
-					 * actual page and drop map count
-					 * to zero.
+					 * The PMD table was unmapped,
+					 * consequently unmapping the folio.
 					 */
 					page_vma_mapped_walk_done(&pvmw);
 					break;
-- 
2.52.0