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[PATCH] mm/migrate_device: fix cache flush when replacing huge zero PMD To: Andrew Morton , Hui Su Cc: apopple@nvidia.com, byungchul@sk.com, david@kernel.org, gourry@gourry.net, joshua.hahnjy@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, matthew.brost@intel.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, ziy@nvidia.com References: <20260817090640.287a9a415da49e3974797aa4@linux-foundation.org> <20260817163646.929678-1-sh_def@163.com> <20260817143415.60bedb09819d13a2dc0fbe63@linux-foundation.org> Content-Language: en-US From: Balbir Singh In-Reply-To: <20260817143415.60bedb09819d13a2dc0fbe63@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MEVPR01CA0053.ausprd01.prod.outlook.com (2603:10c6:220:1fd::8) To CH1PR12MB9670.namprd12.prod.outlook.com (2603:10b6:610:2af::6) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH1PR12MB9670:EE_|SN7PR12MB6689:EE_ 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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 8/18/26 7:34 AM, Andrew Morton wrote: > On Tue, 18 Aug 2026 00:36:46 +0800 Hui Su wrote: > >>>>> --- a/mm/migrate_device.c >>>>> +++ b/mm/migrate_device.c >>>>> @@ -872,7 +872,7 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate, >>>>> >>>>> if (flush) { >>>>> pte_free(vma->vm_mm, pgtable); >>>>> - flush_cache_page(vma, addr, addr + HPAGE_PMD_SIZE); >>>>> + flush_cache_range(vma, addr, addr + HPAGE_PMD_SIZE); >>>>> pmdp_invalidate(vma, addr, pmdp); >>>>> } else { >>>>> pgtable_trans_huge_deposit(vma->vm_mm, pmdp, pgtable); >>>> >>>> Reviewed-by: Balbir Singh >>> >>> doh. It's a shame this actually compiled... >>> >>> Can we add some speculation about the userspace-visible effects of the >>> bug? >>> >>> I'm assuming we should backport the fix? >> >> Hi, >> >> I took a closer look at this, there is no userspace-visible effect today. >> >> The architectures that currently enable ARCH_ENABLE_THP_MIGRATION use >> no-op implementations of flush_cache_page()/flush_cache_range(). >> 32-bit ARM has non-trivial implementations, but does not enable >> ARCH_ENABLE_THP_MIGRATION. >> >> So this appears to be a latent API misuse rather than a currently >> observable bug, and I don't think a stable backport is necessary. > > OK, thanks for checking. > >> Should I resend a v2 clarifying the userspace-visible effect in the >> changelog? > > Yes please, after 7.3-rc1. I have been running some tests at my end, I have some new ones, nothing so far exposes this. Thanks for checking Hui! Balbir