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Sat, 09 May 2026 18:22:44 -0700 (PDT) Date: Sun, 10 May 2026 01:22:43 +0000 From: Wei Yang To: Andrew Morton Cc: Wei Yang , david@kernel.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, sj@kernel.org, ziy@nvidia.com, balbirs@nvidia.com, linux-mm@kvack.org, Lorenzo Stoakes , stable@vger.kernel.org Subject: Re: [PATCH] mm/page_vma_mapped: revalidate and do proper check before return device-private pmd Message-ID: <20260510012243.sz2ex6hzlmdckmmh@master> Reply-To: Wei Yang References: <20260508013728.21285-1-richard.weiyang@gmail.com> <20260508145121.35e2552d403b94ea6f748b90@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260508145121.35e2552d403b94ea6f748b90@linux-foundation.org> User-Agent: NeoMutt/20170113 (1.7.2) X-Stat-Signature: 9najhyxfockx8cdpxtcjmtod8bshtdxd X-Rspamd-Queue-Id: EEAD9180002 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1778376166-314894 X-HE-Meta: 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 Ivo4YUH3 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 08, 2026 at 02:51:21PM -0700, Andrew Morton wrote: >On Fri, 8 May 2026 01:37:28 +0000 Wei Yang wrote: > >> For pmd_trans_huge() and pmd_is_migration_entry(), we does following >> before return the pmd entry: >> >> * re-validate pmd entry >> * check PVMW_MIGRATION >> * check_pmd() >> * handle on pte level if split under us >> >> But for device-private pmd, we just return after pmd_lock(). This may >> lead to improper situation. > >What is "improper situation"? > For example, in remove_migration_pte(), page_vma_mapped_walk() may return device-private entry which is not a migration entry. >> This patch fixes commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration >> support device-private entries") by following the same pattern as >> pmd_trans_huge() and pmd_is_migration_entry(). >> >> Fixes: 65edfda6f3f2 ("mm/rmap: extend rmap and migration support device-private entries") >> Signed-off-by: Wei Yang >> Cc: David Hildenbrand >> Cc: Balbir Singh >> Cc: SeongJae Park >> Cc: Zi Yan >> Cc: Lorenzo Stoakes >> Cc: > >If we're to propose a fix for -stable backporting I believe we should >fully explain to -stable maintainers *why* we're making that proposal. > IIUC, we may do migration on a wrong pmd entry, which may corrupt data. >IOW, and not for the first time(!), what are the worst-case >userspace-visible effects of this bug? > Got it, will pay attention. Sorry for the trouble. -- Wei Yang Help you, Help me