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Thu, 25 Jun 2026 17:44:18 -0700 (PDT) Date: Fri, 26 Jun 2026 00:44:16 +0000 From: Wei Yang To: Balbir Singh Cc: Wei Yang , akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, ziy@nvidia.com, sj@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Lance Yang Subject: Re: [Patch mm-hotfixes v4] mm/page_vma_mapped: fix device-private PMD handling Message-ID: <20260626004416.vm4funxhn42hbi3c@master> Reply-To: Wei Yang References: <20260624065353.1622-1-richard.weiyang@gmail.com> <38410976-ddac-4848-a4ff-e6a9f7d9c828@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <38410976-ddac-4848-a4ff-e6a9f7d9c828@nvidia.com> User-Agent: NeoMutt/20170113 (1.7.2) X-Rspam-User: X-Stat-Signature: bxiunfeu9yftp1eb7yxtrfw85saow8em X-Rspamd-Queue-Id: 4AB6340007 X-Rspamd-Server: rspam06 X-HE-Tag: 1782434661-274085 X-HE-Meta: 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 EFzlE9WP 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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 Thu, Jun 25, 2026 at 09:12:23PM +1000, Balbir Singh wrote: >On 6/24/26 16:53, Wei Yang wrote: >> Commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration support >> device-private entries") introduced the concept of device-private >> PMD entries, but did not correctly update the rmap walk code to >> account for them. >> >> As a result, when page_vma_mapped_walk() encounters device-private >> PMD entries, it takes no action other than to acquire the PMD lock >> and exit. >> >> However this is highly problematic for two reasons - firstly, >> device private entries possess a PFN so check_pmd() needs to be >> called to ensure an overlapping PFN range. >> >> Secondly, and more importantly, if PVMW_MIGRATION is set the >> caller assumes the returned entry is a migration entry, resulting >> in memory corruption when the caller tries to interpret the device >> private entry as such. >> >> In addition, commit 146287290023 ("mm/huge_memory: implement >> device-private THP splitting") allowed device private PMDs to be >> split like THP mappings, but again did not update this code path. >> >> As a result, we might race a PMD split prior to acquiring the PMD >> lock. >> >> This patch addresses all of these issues by invoking check_pmd(), >> ensuring PMVW_MIGRATION is not set and checks whether a split raced >> us we do for PMD THP and migration entries. > >Should be PVMW_MIGRATION and "us we do" -> "as we do" > Hi, Balbir Sorry for missing your comment. Hmm... looks you are right. Andrew, Would you mind handling it or prefer a v2? -- Wei Yang Help you, Help me