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b=WFz4ruk4piV93ZQ4huC8JBMurPzadbXIBA3gZMf2h/UfrQ4PUYGgpDnNOitfoHnKy 0IZaX2o0UZyAEAxtFfUhnvFIi4FsKUROzE1lupgV3Xj7A47Am/9RghcUHL2LugTY9V WR7LvrHSyxKxnf/hstrjZDunmuOMpChsRYmgCsgF4VtbvdfF5elrqe84hVLUK1o0ms tGlKWLJB29JeE1NBWoexrOV8H+9Pzla6PHoExwJuDV0gorXz8Nhj28PewUDMX2aWVJ ANs0Yih2cYD24DRXIpDLbNbd2kDtAvdXs40dbU3RiYtHdrmMrxzVT7hXZXEWgeOApQ XOv7H6rcmxNdg== Date: Tue, 7 Jul 2026 15:01:56 +0100 From: Lorenzo Stoakes To: Usama Arif Cc: Andrew Morton , apopple@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, 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, Balbir Singh Subject: Re: [PATCH 0/3] mm: handle device-private PMDs in walk callbacks Message-ID: References: <20260707135255.292870-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260707135255.292870-1-usama.arif@linux.dev> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: F1B4C120016 X-Stat-Signature: gigo8q697cckn7xn14r3aeurr3tnom6a X-Rspam-User: X-HE-Tag: 1783432930-209227 X-HE-Meta: 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 Mn7j4Kej o0Gp2z5FI3IV5gnHsSTdDGtzEYSBT2q9IPua1GPJtDJ9YMOJ9k09mr8+8CU/j0Pb6WUvCxnZTImThY/UOIk2x7FaDS4CyC42z7tsaKADA0X8iWbwQbDALK1RPvIBoGvNCYQd9xLWLARJ5jRnQKY2XhEKWnBwLbfbHWrfWKqJ1L1tVieEJvOH4+tfzFuontyUisR+fRTO5zvDSR3a6g3XNTn5FZi/J0V96HPnC3sJo5XPgMyNN6O5YsWvNL8drrgOR7dIaLkF9omKLhSpo0SqBuBriAq5/tDo4zEJVpWXEXT2dJNqL/U/oILqvq3j1upRTN3xn+/Tvh8EhDNYQMC9FvheB+3XuMvPUrxrFQCfqYHB3ee+M/aB9UrZ8yntnoF6L+4JI Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: +cc Balbir Thanks for the series! I think Balbir should be cc'd no? On Tue, Jul 07, 2026 at 06:45:06AM -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. > > The first 2 fixes were reported as pre-existing issues by sashiko in my > PMD swap entry series [1]. Hopefully sashiko won't point these out > in the next PMD swap entry series :) Yeah I don't love these 'existing problem' reports (distracting from other work, add workload, really it feels like that should be a passive reporting mode for sashiko not arbitrarily added to other series), but sending it as a separate series is indeed the right way :) These of course should never block an unrelated series. > > [1] https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=6 Hmm we've had a whole host of issues with device-private PMDs recently. Balbir - would it be possible to audit all of the code paths and proactively see if there's anything else that could hit problems here? > > Usama Arif (3): > mm/mempolicy: skip device-private PMDs when queueing folios > mm/madvise: skip device-private PMDs in cold and pageout walks > mm/huge_memory: skip device-private PMDs in madvise_free_huge_pmd > > mm/huge_memory.c | 3 +++ > mm/madvise.c | 3 +++ > mm/mempolicy.c | 2 ++ > 3 files changed, 8 insertions(+) > > -- > 2.53.0-Meta > Cheers, Lorenzo