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Mon, 03 Oct 2022 16:25:33 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.120.41.1.1\)) Subject: Re: [PATCH v2 12/39] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW From: Nadav Amit In-Reply-To: <65CF3B29-BF53-4BA3-89D9-5398CEB7F813@gmail.com> Date: Mon, 3 Oct 2022 16:25:27 -0700 Cc: "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "Yu, Yu-cheng" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "jannh@google.com" , "dethoma@microsoft.com" , "linux-arch@vger.kernel.org" , "kcc@google.com" , "bp@alien8.de" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , Andy Lutomirski , "pavel@ucw.cz" , "arnd@arndb.de" , "Moreira, Joao" , Thomas Gleixner , "mike.kravetz@oracle.com" , "x86@kernel.org" , "linux-doc@vger.kernel.org" , "jamorris@linux.microsoft.com" , "john.allen@amd.com" , "rppt@kernel.org" , "mingo@redhat.com" , "Shankar, Ravi V" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" Content-Transfer-Encoding: quoted-printable Message-Id: References: <20220929222936.14584-1-rick.p.edgecombe@intel.com> <20220929222936.14584-13-rick.p.edgecombe@intel.com> <64313344833c3b1701002a347d539e69276b66fb.camel@intel.com> <35EEB9F0-D99A-4664-9628-27029B52CFD1@gmail.com> <65CF3B29-BF53-4BA3-89D9-5398CEB7F813@gmail.com> To: "Edgecombe, Rick P" X-Mailer: Apple Mail (2.3696.120.41.1.1) ARC-Message-Signature: i=1; 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dkim=pass header.d=gmail.com header.s=20210112 header.b=JCoc10Eh; spf=pass (imf23.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.216.48 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 21DCE140011 X-Rspam-User: X-Stat-Signature: 346qtntoqziunwqtx1ij4zfusg1ep83e X-HE-Tag: 1664839534-850780 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: On Oct 3, 2022, at 4:20 PM, Nadav Amit wrote: > On Oct 3, 2022, at 4:17 PM, Nadav Amit wrote: >=20 >> On Oct 3, 2022, at 3:28 PM, Edgecombe, Rick P = wrote: >>=20 >>> On Mon, 2022-10-03 at 11:11 -0700, Nadav Amit wrote: >>>> Did you have a look at ptep_set_access_flags() and friends and >>>> checked they >>>> do not need to be changed too?=20 >>>=20 >>> ptep_set_access_flags() doesn't actually set any additional dirty = bits >>> on x86, so I think it's ok. >>=20 >> Are you sure about that? (lost my confidence today so I am hesitant). >>=20 >> Looking on insert_pfn(), I see: >>=20 >> entry =3D maybe_mkwrite(pte_mkdirty(entry), = vma); >> if (ptep_set_access_flags(vma, addr, pte, = entry, 1)) ... >>=20 >> This appears to set the dirty bit while potentially leaving the = write-bit >> clear. This is the scenario you want to avoid, no? >=20 > No. I am not paying attention. Ignore. Sorry for the spam. Just this =E2=80=9Cdirty=E2=80=9D argument is = confusing. This indeed seems like a flow that can set the dirty bit. I think.