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Sun, 30 Aug 2026 05:18:39 +0000 X-Mizu-Trace-ID: 82afb8ac5ccba36e X-Migadu-Flow: FLOW_OUT Message-ID: Date: Sun, 30 Aug 2026 13:18:24 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/3] mm: reject zone device folios in more folio walkers To: Andrew Morton Cc: gourry@gourry.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, david@kernel.org, ljs@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, vbabka@kernel.org, jannh@google.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, balbirs@nvidia.com References: <20260817220810.1175596-1-gourry@gourry.net> <20260818043143.22297-1-lance.yang@linux.dev> <20260829171819.e1e8910e7e9a8a46b87c870f@linux-foundation.org> Content-Language: en-US From: Lance Yang In-Reply-To: <20260829171819.e1e8910e7e9a8a46b87c870f@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 6A1E81C0007 X-Stat-Signature: mw58qn3r1g7qzkinsqqdjqzscts3cb61 X-Rspam-User: X-HE-Tag: 1788067122-162304 X-HE-Meta: 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 9OTJnqJR AEldXwczypTxBOup6wxfBSjYBsXgnZAN+L7hR0lPaLf9y04bJrrcxK5DokyxUp3pw9GJoRzfIc3p+5/jBdN7lMR/W5MpIpAGw+udBHRCsarQ3JUBkm34Gt2BFl3Rz9gNKhBK6tfVzpKkxvkWQIiRu8ZOvD9dzvgpy4mM0BaYii2LNygIdfP03iMQTbQIPT8mUcVMQg10yVwehDGzFj6/qGtS9TnItwmK0NBy2O+aaxiwk5OQKtWzs93K2Dpic2X1ukQ0u2JcUPS0vmY57rdL5pPJGmPvCIlqaGezpcZESmypQWrWVv7+nGp6sx+LlFrdesvD3UfsxXsG73/ul3IDKPbqhr2UvohPBCJZonz6l4+uLRZGPg6UbpXSotIhX7g3n9ZiFV519g3jK7Hk/3rg1rSdflneuFTbAWsBbdijz2X+ASTg8baG9LuNk4a9HEr3fwOy6pt5xAdso3sCEqa+dOyM25N/VlX+FakId Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/8/30 08:18, Andrew Morton wrote: > On Tue, 18 Aug 2026 12:31:43 +0800 Lance Yang wrote: > >> >> On Mon, Aug 17, 2026 at 06:08:07PM -0400, Gregory Price wrote: >>> Several LRU-oriented mm walkers resolve the folio backing a PMD entry >>> (or a physical pfn) and then reclaim, age, migrate, or lazyfree it >>> without ever checking for ZONE_DEVICE memory. >>> >>> This series adds missing folio_is_zone_device() rejections, matching >>> the checks that comparable walkers already perform. >>> >>> - mm/huge_memory, mm/madvise: the !pmd_present branch above these sites >>> only filters device-private entries (which are non-present). >>> >>> A present zone device PMD (e.g. device-coherent) would still reach the >>> folio and be lazyfreed / aged / paged out. Add an explicit check. >>> >>> - mm/mempolicy: queue_folios_pmd() can see a present zone device PMD >>> (e.g. device-coherent) and queue it for migration. >>> >>> No crash reproducer - this is a correctness/hardening cleanup found by >>> inspection. All checks are placed after the folio is resolved and before >>> it is acted upon, on paths that already hold the relevant page-table lock, >>> so no locking or refcount changes are involved. >> >> Cool! >> >> Gave the whole series a spin on x86_64 QEMU with a PMD-mapped >> device-coherent THP. Without these patches, partial MADV_FREE and >> MADV_COLD reliably hit a kernel panic in remove_migration_pte(), while >> mbind(MPOL_MF_MOVE | MPOL_MF_STRICT) returned -EIO. >> >> With v2, all three worked fine, PMD mapping stayed intact, and data >> checked out :) >> >> Note that both kernels used the same small change to the in-kernel HMM >> test driver, allowing its coherent device memory to be allocated as 2 MB >> folios so the PMD-mapped test case could be exercised. >> >> Tested-by: Lance Yang > > Thanks Lance, you're so diligent. > > I'm wondering what to do here. Gregory told us > > : No crash reproducer - this is a correctness/hardening cleanup found by > : inspection. All checks are placed after the folio is resolved and before > : it is acted upon, on paths that already hold the relevant page-table lock, > : so no locking or refcount changes are involved. > > And you had to tweak the hmm-test driver to reproduce the bug(s). > > So when do we push this series out to -stable? As a hair-on-fire > hotfix, or as a leisurely next-merge-window thing? Thanks, Andrew :) Yeah, I'd say next merge window should be fine :) The crash is real once the mapping exists, but I had to tweak test_hmm to create that PMD-mapped device-coherent folio, and I couldn't find any in-tree production driver doing that today. So no need to rush this one, I guess. > > And Sashiko was clearly having a bad day, able to find only nine > pre-existing things to shout about: > https://sashiko.dev/#/patchset/20260817220810.1175596-1-gourry@gourry.net >