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Sun, 22 Mar 2026 04:29:55 -0700 (PDT) Received: from localhost ([240d:1a:c0d:9f00:be24:11ff:fe35:71b3]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82b03bbebb2sm7205704b3a.14.2026.03.22.04.29.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 22 Mar 2026 04:29:55 -0700 (PDT) From: Shigeru Yoshida To: Andrew Morton Cc: Minchan Kim , Sergey Senozhatsky , Mark-PK Tsai , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/zsmalloc: copy KMSAN metadata in zs_page_migrate() In-Reply-To: <20260321104845.452d0f903a52d45d3b76894e@linux-foundation.org> (Andrew Morton's message of "Sat, 21 Mar 2026 10:48:45 -0700") References: <20260321132912.93434-1-syoshida@redhat.com> <20260321104845.452d0f903a52d45d3b76894e@linux-foundation.org> User-Agent: mu4e 1.12.12; emacs 30.2 Date: Sun, 22 Mar 2026 20:29:54 +0900 Message-ID: <87h5q8qez1.fsf@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Andrew Morton writes: > On Sat, 21 Mar 2026 22:29:11 +0900 Shigeru Yoshida wrote: > >> zs_page_migrate() uses copy_page() to copy the contents of a zspage >> page during migration. However, copy_page() is not instrumented by >> KMSAN, so the shadow and origin metadata of the destination page are >> not updated. >> >> As a result, subsequent accesses to the migrated page are reported >> as use-after-free by KMSAN, despite the data being correctly copied. >> >> Add a kmsan_copy_page_meta() call after copy_page() to propagate the >> KMSAN metadata to the new page, matching what copy_highpage() does >> internally. >> >> Fixes: afb2d666d025 ("zsmalloc: use copy_page for full page copy") > > That's three years old. Can anyone suggest why this has only now been > discovered? I think it's because KMSAN is clang and x86-64-only, so very few people run it. Also, this only triggers when compaction actually migrates a zspage page, which needs significant memory pressure. Shigeru