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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-92ee5d375fesm815846285a.37.2026.07.12.05.41.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 12 Jul 2026 05:41:01 -0700 (PDT) Date: Sun, 12 Jul 2026 08:40:56 -0400 From: Gregory Price To: Usama Arif Cc: Andrew Morton , apopple@nvidia.com, balbirs@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, david@kernel.org, dev.jain@arm.com, 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, sashiko-bot , stable@vger.kernel.org Subject: Re: [PATCH v3 2/3] mm/madvise: skip device-private PMDs in cold and pageout walks Message-ID: References: <20260710105557.1987433-1-usama.arif@linux.dev> <20260710105557.1987433-3-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260710105557.1987433-3-usama.arif@linux.dev> X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B171B140003 X-Stat-Signature: wktbn8e9z6cymj33k9pqcmd9z5o99uug X-HE-Tag: 1783860062-952259 X-HE-Meta: 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 JA/u2BGO 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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, Jul 10, 2026 at 03:55:22AM -0700, Usama Arif wrote: > madvise_cold_or_pageout_pte_range() takes pmd_trans_huge_lock(), whose > pmd_is_huge() check returns true for a device-private PMD. The subsequent > !pmd_present() branch has a VM_BUG_ON() asserting migration is the only > allowed non-present case; a device-private PMD trips it. > > Skip device-private PMDs in that non-present branch and continue to > huge_unlock before calling pmd_folio(). Downgrade the check to > VM_WARN_ON_ONCE() so an unexpected PMD softleaf logs a warning rather > than panicking. Drop the thp_migration_supported() guard: it expands to > IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_SOFTLEAF), and both > pmd_is_migration_entry() and pmd_is_device_private_entry() already > return false when that config is not selected, so the guard suppresses > only the case where the warning would already be silent. > > Potential trigger: an HMM-based GPU driver races with > madvise(MADV_COLD)/MADV_PAGEOUT: pmd_trans_huge(*pmd) reads true, then > migrate_vma_pages() flips the PMD to a device-private entry before the > PMD lock is acquired. > > Reported-by: sashiko-bot > Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=6 > Fixes: 368076f52ebe ("mm/huge_memory: add device-private THP support to PMD operations") > Cc: > Reviewed-by: Joshua Hahn > Reviewed-by: Zi Yan > Reviewed-by: Balbir Singh > Signed-off-by: Usama Arif Reviewed-by: Gregory Price