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Peter Anvin" , Andrew Morton Subject: Re: [PATCH v1] x86/mm/pat: fix VM_PAT handling in COW mappings Message-ID: References: <20240312181118.318701-1-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240312181118.318701-1-david@redhat.com> X-Stat-Signature: ygb5iy8b56hf8heq6wstjryz7eo4zy37 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 8883B40013 X-Rspam-User: X-HE-Tag: 1710271381-41429 X-HE-Meta: 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 DxpLpLbX z0UQqex2o7e0eqZg8AAhM6m4BJh+/Ud3e8dKdbHDSK4iup1ZdEk5LxW8GOnac6OXtnmItVInVcawyoSjKJXs9oH2nKw7LxJfXE+yKHUWv2eqeS9gH71M6/HMqJnEYVLcf7M1FnNfbrTybpe54jTs/A4xoSmT0UbOSqiYk1BOPdyTHhdi07sF23dJdUw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 12, 2024 at 07:11:18PM +0100, David Hildenbrand wrote: > PAT handling won't do the right thing in COW mappings: the first PTE > (or, in fact, all PTEs) can be replaced during write faults to point at > anon folios. Reliably recovering the correct PFN and cachemode using > follow_phys() from PTEs will not work in COW mappings. I guess the first question is: Why do we want to support COW mappings of VM_PAT areas? What breaks if we just disallow it?