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([2601:646:c200:1ef2:6cf1:fbba:cb42:db60]) by smtp.gmail.com with ESMTPSA id bt18sm3110564pjb.1.2019.08.13.16.49.30 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 13 Aug 2019 16:49:30 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v8 11/27] x86/mm: Introduce _PAGE_DIRTY_SW From: Andy Lutomirski X-Mailer: iPhone Mail (16G77) In-Reply-To: Date: Tue, 13 Aug 2019 16:49:29 -0700 Cc: Yu-cheng Yu , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin Content-Transfer-Encoding: quoted-printable Message-Id: <08A983E6-7B9C-4BDF-887A-F57734FADC9E@amacapital.net> References: <20190813205225.12032-1-yu-cheng.yu@intel.com> <20190813205225.12032-12-yu-cheng.yu@intel.com> To: Dave Hansen 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 Aug 13, 2019, at 4:02 PM, Dave Hansen wrote: >>=20 >> static inline pte_t pte_mkwrite(pte_t pte) >> { >> + pte =3D pte_move_flags(pte, _PAGE_DIRTY_SW, _PAGE_DIRTY_HW); >> return pte_set_flags(pte, _PAGE_RW); >> } >=20 > It also isn't clear to me why this *must* move bits here. Its doubly > unclear why you would need to do this on systems when shadow stacks are > compiled in but disabled. Why is it conditional at all? ISTM, in x86, RO+dirty has been effectively r= epurposed. To avoid having extra things that can conditionally break, I thin= k this code should be unconditional.=20 That being said, I=E2=80=99m not at all sure that pte_mkwrite on a shadow st= ack page makes any sense. > >=20 > Same comments for pmds and puds. Wasn=E2=80=99t Kirill working on a rework if the whole page table system to j= ust have integer page table levels?=