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b=NsUIgn8VbdmC+39Tq3LQvej3JpwRFehOwuE7dvt9ybC6OLwBNz9KZYvARZh5M5664 Z1/k3tEEVvARkQmBZO9lNZvJOGoDouks8FeiCaUpb8plCUdIfjP5gCN9+ISyu+E0h2 Ufv8DJnbHqn/TRaC928KcRv1sRgQF4/P4jTMGo4A= Date: Mon, 17 Aug 2026 14:34:15 -0700 From: Andrew Morton To: Hui Su Cc: apopple@nvidia.com, balbirs@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 Subject: Re: [PATCH] mm/migrate_device: fix cache flush when replacing huge zero PMD Message-Id: <20260817143415.60bedb09819d13a2dc0fbe63@linux-foundation.org> In-Reply-To: <20260817163646.929678-1-sh_def@163.com> References: <20260817090640.287a9a415da49e3974797aa4@linux-foundation.org> <20260817163646.929678-1-sh_def@163.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: u1a1o3b75ekq8fn19yyqazhbn5i1aj8c X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 14620180007 X-HE-Tag: 1787002457-111745 X-HE-Meta: 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 bO++tfFk adsACTIYHhkWxvgHgViAlbjndt5KnJiJs2xIIWN8wtqsbOJYjSULdSXjgS0jr3XQ8HHV1E6c4pCjF+LstOF+h5yF+ikhchUhzMu24ubES3DhjiGy4xANqKAlLgEPTcsNEhwTx0B74BQenJ07Wo5X5vBpRnXRXRO36L5PK8uo/4KPBNPDVyhroiNDBDLpvYxsG2W0XD363GPtDDkk7L79zOZFkMocVcI8Mey9IqgQ6del8xG2srMz6IKjnwHxBIXStXQYKrBggQjllUf5XJip3/8ruhTZzi1DPFnRvtOa1TAFeiOLbMqJW8DPVoPqYlNje0LEl4trrWZvlOQN+TTfQvDlOLWCHyldthhhSnFimyzGt8r9GTSN/QSJ33vpvzAN4o5NOURkqzUG9CdPEihFEZW2ce4G5iqfPRf9U Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.