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Mon, 03 Oct 2022 17:40:36 -0700 (PDT) Content-Type: text/plain; charset=us-ascii 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: <547f2a8a87c255c58dbf2350013f72649dfcdc10.camel@intel.com> Date: Mon, 3 Oct 2022 17:40:33 -0700 Cc: "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "Yu, Yu-cheng" , "Eranian, Stephane" , "kirill.shutemov@linux.intel.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "jannh@google.com" , "dethoma@microsoft.com" , "kcc@google.com" , "linux-arch@vger.kernel.org" , "pavel@ucw.cz" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , Andy Lutomirski , "jamorris@linux.microsoft.com" , "arnd@arndb.de" , "Moreira, Joao" , Thomas Gleixner , "bp@alien8.de" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "linux-doc@vger.kernel.org" , "rppt@kernel.org" , "john.allen@amd.com" , "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> <547f2a8a87c255c58dbf2350013f72649dfcdc10.camel@intel.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=pqGdfqbW; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf19.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.216.52 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com X-Rspamd-Server: rspam01 X-HE-Tag: 1664844037-428571 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 4:38 PM, Edgecombe, Rick P = wrote: > I think the HW dirty bit will not be set here. How it works is, > pte_mkdirty() will not actually set the HW dirty bit, but instead the > software COW bit. Here is the relevant snippet: >=20 > static inline pte_t pte_mkdirty(pte_t pte) > { > pteval_t dirty =3D _PAGE_DIRTY; >=20 > /* Avoid creating Dirty=3D1,Write=3D0 PTEs */ > if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !pte_write(pte)) > dirty =3D _PAGE_COW; >=20 > return pte_set_flags(pte, dirty | _PAGE_SOFT_DIRTY); > } >=20 > So for a !VM_WRITE vma, you end up with Write=3D0,Cow=3D1 PTE passed > into ptep_set_access_flags(). Does it make sense? Thanks for your patience with me. I should have read the series in = order.