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04 Oct 2022 07:18:45 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10490"; a="623945386" X-IronPort-AV: E=Sophos;i="5.95,158,1661842800"; d="scan'208";a="623945386" Received: from samrober-mobl.amr.corp.intel.com (HELO [10.209.85.136]) ([10.209.85.136]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Oct 2022 07:18:44 -0700 Message-ID: <62c6c3a7-3bd2-69ee-36cd-341e11c43978@intel.com> Date: Tue, 4 Oct 2022 07:18:43 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v2 06/39] x86/fpu: Add helper for modifying xstate Content-Language: en-US To: "Edgecombe, Rick P" , "keescook@chromium.org" Cc: "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.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" , "Lutomirski, Andy" , "pavel@ucw.cz" , "arnd@arndb.de" , "Moreira, Joao" , "tglx@linutronix.de" , "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" References: <20220929222936.14584-1-rick.p.edgecombe@intel.com> <20220929222936.14584-7-rick.p.edgecombe@intel.com> <202210031045.419F7DB396@keescook> From: Dave Hansen In-Reply-To: Content-Type: text/plain; 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bh=/ZhcxE23XxY+wRDapL4hQYTPECwVP1wjdbRokWF4C6M=; b=VUZPqHzyBnQP3NDShxAK0phmuyIwpapQAhS6fUWUJQCfq2eFMuVEHQrsqmbIAX1OaLR73g QoawTW0ekFDZQFSYykg7n8iuEQ12p+SIfN/wLHdh9h2LvgLn4TH+Ip0X0DH5wCj/7nTzV+ ydLXA+wqH97CSZIswjwau4gFGl3Mob8= X-Rspam-User: Authentication-Results: imf23.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b="Klej00/g"; dmarc=pass (policy=none) header.from=intel.com; spf=pass (imf23.hostedemail.com: domain of dave.hansen@intel.com designates 192.55.52.120 as permitted sender) smtp.mailfrom=dave.hansen@intel.com X-Stat-Signature: adftqoca47qwkd95yoctkn8ry6rkjiyg X-Rspamd-Queue-Id: 06C60140021 X-Rspamd-Server: rspam09 X-HE-Tag: 1664893126-347969 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 10/3/22 13:05, Edgecombe, Rick P wrote: > The CET state is xsaves managed. It gets lazily restored before > returning to userspace with the rest of the fpu stuff. This function > will force restore all the fpu state to the registers early and lock > them from being automatically saved/restored. Then the tasks CET state > can be modified in the MSRs, before unlocking the fpregs. Last time I > tried to modify the state directly in the xsave buffer when it was > efficient, but it had issues and Thomas suggested this. Can you get the gist of this in a comment, please?