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([2600:1010:b00c:70fb:70e6:7ca0:457a:d080]) by smtp.gmail.com with ESMTPSA id d123sm3359464pfc.144.2019.06.28.14.49.33 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 28 Jun 2019 14:49:33 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (1.0) Subject: Re: [RFC PATCH 1/3] mm: Introduce VM_IBT for CET legacy code bitmap From: Andy Lutomirski X-Mailer: iPhone Mail (16F203) In-Reply-To: <20190628194158.2431-1-yu-cheng.yu@intel.com> Date: Fri, 28 Jun 2019 14:49:32 -0700 Cc: 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: References: <20190628194158.2431-1-yu-cheng.yu@intel.com> To: Yu-cheng Yu 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 Jun 28, 2019, at 12:41 PM, Yu-cheng Yu wrote: >=20 > The previous discussion of the IBT legacy code bitmap is here: >=20 > https://lkml.org/lkml/2019/6/6/1032 >=20 > When CET Indirect Branch Tracking (IBT) is enabled, the processor expects > every branch target is an ENDBR instruction, or the target's address is > marked as legacy in the legacy code bitmap. The bitmap covers the whole > user-mode address space (TASK_SIZE_MAX for 64-bit, TASK_SIZE for IA32), > and each bit represents one page of linear address range. >=20 > This patch introduces VM_IBT for the bitmap. There=E2=80=99s no need to allocate a bit for this and to clutter up the fau= lt code with special cases. Use _install_special_mapping(), please. If you n= eed to make it more flexible to cover your use case, please do so.