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[24.6.216.183]) by smtp.gmail.com with ESMTPSA id q15-20020a17090ad38f00b00209a12b3879sm6955729pju.37.2022.10.03.18.56.16 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 03 Oct 2022 18:56:18 -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 17/39] mm: Fixup places that call pte_mkwrite() directly From: Nadav Amit In-Reply-To: <20220929222936.14584-18-rick.p.edgecombe@intel.com> Date: Mon, 3 Oct 2022 18:56:15 -0700 Cc: X86 ML , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , linux-doc@vger.kernel.org, Linux MM , linux-arch , linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H . J . Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V . Shankar" , Weijiang Yang , "Kirill A . Shutemov" , joao.moreira@intel.com, John Allen , kcc@google.com, eranian@google.com, Mike Rapoport , jamorris@linux.microsoft.com, dethoma@microsoft.com, Yu-cheng Yu Content-Transfer-Encoding: quoted-printable Message-Id: <96BFE665-4A76-4CE0-A22B-A999C4A16FFD@gmail.com> References: <20220929222936.14584-1-rick.p.edgecombe@intel.com> <20220929222936.14584-18-rick.p.edgecombe@intel.com> To: Rick Edgecombe X-Mailer: Apple Mail (2.3696.120.41.1.1) Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Hopefully I will not waste your time again=E2=80=A6 If it has been = discussed in the last 26 iterations, just tell me and ignore. On Sep 29, 2022, at 3:29 PM, Rick Edgecombe = wrote: > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -606,8 +606,7 @@ static void migrate_vma_insert_page(struct = migrate_vma *migrate, > goto abort; > } > entry =3D mk_pte(page, vma->vm_page_prot); > - if (vma->vm_flags & VM_WRITE) > - entry =3D pte_mkwrite(pte_mkdirty(entry)); > + entry =3D maybe_mkwrite(pte_mkdirty(entry), vma); > } This is not exactly the same logic. You might dirty read-only pages = since you call pte_mkdirty() unconditionally. It has been known not to be very robust (e.g., dirty-COW and friends). Perhaps it is not dangerous = following some recent enhancements, but why do you want to take the risk? Instead, although it might seem redundant, the compiler will hopefully = would make it efficient: if (vma->vm_flags & VM_WRITE) { entry =3D pte_mkdirty(entry); entry =3D maybe_mkwrite(entry, vma); }