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b=REiuFs4VZ8HBHgEuS8pPATEsHkD67CqvsVug2ISH3ua+FB7HXhRIT42SsJ522Cw+R 4RqPTXUcoSl3sv9Nx0CKFVeyB/CD/AOjA+DBcmQVnwjcj3BAB7XLv8oNxPSn2XhyYx Nb5shhdV5JTt0cIfb3ciLGYnVvFYGsDsaTGMTEZw= Date: Fri, 10 Jul 2026 16:53:48 -0700 From: Andrew Morton To: Usama Arif Cc: apopple@nvidia.com, balbirs@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, jannh@google.com, joshua.hahnjy@gmail.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, matthew.brost@intel.com, npache@redhat.com, rakie.kim@sk.com, ryan.roberts@arm.com, vbabka@kernel.org, ying.huang@linux.alibaba.com, ziy@nvidia.com, shakeel.butt@linux.dev, hannes@cmpxchg.org Subject: Re: [PATCH v3 0/3] mm: handle device-private PMDs in walk callbacks Message-Id: <20260710165348.cab6f58aa81b30e34d121d0d@linux-foundation.org> In-Reply-To: <20260710105557.1987433-1-usama.arif@linux.dev> References: <20260710105557.1987433-1-usama.arif@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: BC94A40007 X-Stat-Signature: jycmn5469exaashtut77chud7swf3rss X-HE-Tag: 1783727630-946906 X-HE-Meta: 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 NiBbbH06 J22kOhJxt3kHUZeVaW0noQth9OCfMAkri2Sk2ZzDdSl7CXphdCt9+Af+dSzR+5B0uC98zYvxxIibXDLM9e1EholRuiG1rvVMrVdad0LNiOcCc92PD13weigsaECyEuhYMWMPSPudJrW4U0NKyx3VO01wwCxz0cV+Qr/Wm/6TAND/OdplLjsB4b11gtkgK28S8ZQlq9mKWLsuNv8mjw2ghH74uQwhNqSk9+jOZa8e5m/xrkFc2ujsCgr7q+11rp+rXACqT7K73nPRE2tP0As1CLJej2lg7F0GwiYXsDcAANJ+0jt5lsGegvi6+aTtW718OqVp8PDNpAABvO4cj5QWL1zdzDE/IzHhETILTdTk4mH+auhp/n1QwcOmmfiJ+3zHcIMqf Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 10 Jul 2026 03:55:20 -0700 Usama Arif wrote: > Since commit 368076f52ebe ("mm/huge_memory: add device-private THP support > to PMD operations") a PMD may hold a device-private swap entry whenever > an HMM-based GPU driver migrates an anonymous THP folio to device memory > via migrate_vma_pages(). > > pmd_trans_huge_lock() succeeds for such PMDs (pmd_is_huge() returns true > for any non-present, non-none huge PMD), so several MM walk callbacks > that used to assume present THP or migration entry are now reachable with > a device-private PMD. The results range from a VM_BUG_ON() firing on debug > kernels, to an oops on a bogus vmemmap dereference, to silently isolating > an unrelated live folio from LRU in the aliasing case. Added, thanks. I didn't add these as hotfixes - the Fixes: commit is somewhat old. Feel free to disagree with this! Sashiko went nuts over possible pre-existing issues: https://sashiko.dev/#/patchset/20260710105557.1987433-1-usama.arif@linux.dev