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[2003:cb:c706:e00:8d96:5dba:6bc4:6e89]) by smtp.gmail.com with ESMTPSA id l14-20020adff48e000000b0021d7ad6b9fdsm16603709wro.57.2022.07.20.11.11.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Jul 2022 11:11:20 -0700 (PDT) Message-ID: Date: Wed, 20 Jul 2022 20:11:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [RFC PATCH 01/14] userfaultfd: set dirty and young on writeprotect Content-Language: en-US To: Nadav Amit Cc: Linux MM , LKML , Andrew Morton , Mike Rapoport , Axel Rasmussen , Andrea Arcangeli , Andrew Cooper , Andy Lutomirski , Dave Hansen , Peter Xu , Peter Zijlstra , Thomas Gleixner , Will Deacon , Yu Zhao , Nick Piggin References: <20220718120212.3180-1-namit@vmware.com> <20220718120212.3180-2-namit@vmware.com> <09d84297-65d5-a3df-fdc0-a7168cdb0798@redhat.com> <99AFB0A0-B2F8-420A-8164-1705EC14B255@vmware.com> <97e82e31-2411-501e-d401-d175eb24642f@redhat.com> <18EDDBB1-255A-475F-812A-8CA947493EC8@vmware.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <18EDDBB1-255A-475F-812A-8CA947493EC8@vmware.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20.07.22 20:09, Nadav Amit wrote: > On Jul 20, 2022, at 11:00 AM, David Hildenbrand wrote: > >> My patch review skills have seen better days. I thought you'd be >> removing the pte_write() check ... :( Tired eyes ... >> >>> Having said that, I do notice now that pte_mkdirty() should not be done >>> only this condition is fulfilled. Instead we should just have >>> something like: >>> >>> if (will_need) { >>> ptent = pte_mkyoung(ptent); >>> if (pte_write(ptent)) >>> ptent = pte_mkdirty(ptent); >>> } >> >> As can_change_pte_writable() will fail if it stumbles over a !pte_dirty >> page in current code ... so I assume you would have that code before the >> actual pte_mkwrite() logic, correct? > > No, I thought this should go after for 2 reasons: > > 1. You want to allow the PTE to be made writable following the > can_change_pte_writable(). > > 2. You do not want to set a non-writable PTE as dirty, especially since it > might then be used to determine that the PTE can become writable. Doing so > would circumvent cases in which set_page_dirty() needs to be called and > break things down. The I'm confused how can_change_pte_writable() would ever allow for that. Best to show me the code :) -- Thanks, David / dhildenb