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[PATCH] mm/page_vma_mapped: revalidate and do proper check before return device-private pmd To: 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, sj@kernel.org, ziy@nvidia.com Cc: linux-mm@kvack.org, Lorenzo Stoakes , stable@vger.kernel.org References: <20260508013728.21285-1-richard.weiyang@gmail.com> Content-Language: en-US From: Balbir Singh In-Reply-To: <20260508013728.21285-1-richard.weiyang@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MEWPR01CA0195.ausprd01.prod.outlook.com (2603:10c6:220:1e9::13) To PH8PR12MB7277.namprd12.prod.outlook.com (2603:10b6:510:223::13) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR12MB7277:EE_|SJ1PR12MB6313:EE_ X-MS-Office365-Filtering-Correlation-Id: 34402a53-9f03-459f-7fcd-08dead53f5b3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 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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 5/8/26 11:37, Wei Yang wrote: > For pmd_trans_huge() and pmd_is_migration_entry(), we does following > before return the pmd entry: > > * re-validate pmd entry > * check PVMW_MIGRATION > * check_pmd() > * handle on pte level if split under us > > But for device-private pmd, we just return after pmd_lock(). This may > lead to inproper situation. > Could you elaborate a more on the improper situation? > This patch fixes commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration > support device-private entries") by following the same pattern as > pmd_trans_huge() and pmd_is_migration_entry(). > > Fixes: 65edfda6f3f2 ("mm/rmap: extend rmap and migration support device-private entries") > Signed-off-by: Wei Yang > Cc: David Hildenbrand > Cc: Balbir Singh > Cc: SeongJae Park > Cc: Zi Yan > Cc: Lorenzo Stoakes > Cc: > --- > mm/page_vma_mapped.c | 34 +++++++++++++++++++++++----------- > 1 file changed, 23 insertions(+), 11 deletions(-) > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index a4d52fdb3056..5d337ea43019 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -269,21 +269,33 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > spin_unlock(pvmw->ptl); > pvmw->ptl = NULL; > } else if (!pmd_present(pmde)) { > - const softleaf_t entry = softleaf_from_pmd(pmde); > + softleaf_t entry = softleaf_from_pmd(pmde); > > if (softleaf_is_device_private(entry)) { > pvmw->ptl = pmd_lock(mm, pvmw->pmd); > - return true; > - } > - > - if ((pvmw->flags & PVMW_SYNC) && > - thp_vma_suitable_order(vma, pvmw->address, > - PMD_ORDER) && > - (pvmw->nr_pages >= HPAGE_PMD_NR)) > - sync_with_folio_pmd_zap(mm, pvmw->pmd); > + entry = softleaf_from_pmd(*pvmw->pmd); > + > + if (softleaf_is_device_private(entry)) { Do we need to check softleaf_is_device_private() twice, can't we hold the pmd lock and check once? > + if (pvmw->flags & PVMW_MIGRATION) > + return not_found(pvmw); Double check, do we want to skip migration pte's (from remove_migration_pte) > + if (!check_pmd(softleaf_to_pfn(entry), pvmw)) > + return not_found(pvmw); > + return true; > + } > > - step_forward(pvmw, PMD_SIZE); > - continue; > + /* THP pmd was split under us: handle on pte level */ > + spin_unlock(pvmw->ptl); > + pvmw->ptl = NULL; > + } else { > + if ((pvmw->flags & PVMW_SYNC) && > + thp_vma_suitable_order(vma, pvmw->address, > + PMD_ORDER) && > + (pvmw->nr_pages >= HPAGE_PMD_NR)) > + sync_with_folio_pmd_zap(mm, pvmw->pmd); > + > + step_forward(pvmw, PMD_SIZE); > + continue; > + } > } > if (!map_pte(pvmw, &pmde, &ptl)) { > if (!pvmw->pte) How was this tested? Did you run hmm-tests? Is there a broken user space that caught the issue? Balbir Singh