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([2001:b07:6468:f312:bd61:914:5c2f:2580]) by smtp.gmail.com with ESMTPSA id n6sm6483443wrs.81.2020.04.07.15.12.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Apr 2020 15:12:16 -0700 (PDT) Subject: Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation To: Peter Zijlstra , Nadav Amit Cc: Thomas Gleixner , LKML , hch@infradead.org, Sean Christopherson , mingo , bp , hpa@zytor.com, x86 , "Kenneth R. Crudup" , Jessica Yu , Rasmus Villemoes , Fenghua Yu , Xiaoyao Li , Thomas Hellstrom , Tony Luck , Steven Rostedt , Greg Kroah-Hartman , jannh@google.com, keescook@chromium.org, David.Laight@aculab.com, Doug Covelli , mhiramat@kernel.org References: <20200407110236.930134290@infradead.org> <20200407111007.429362016@infradead.org> <10ABBCEE-A74D-4100-99D9-05B4C1758FF6@gmail.com> <20200407193853.GP2452@worktop.programming.kicks-ass.net> <90B32DAE-0BB5-4455-8F73-C43037695E7C@gmail.com> <20200407205042.GT2452@worktop.programming.kicks-ass.net> <96C2F23A-D6F4-4A04-82B6-284788C5D2CC@gmail.com> <20200407212754.GU2452@worktop.programming.kicks-ass.net> From: Paolo Bonzini Message-ID: Date: Wed, 8 Apr 2020 00:12:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200407212754.GU2452@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/04/20 23:27, Peter Zijlstra wrote: > On Tue, Apr 07, 2020 at 02:22:11PM -0700, Nadav Amit wrote: >> Anyhow, I do not think it is the only use-case which is not covered by your >> patches (even considering CRs/DRs alone). For example, there is no kernel >> function to turn on CR4.VMXE, which is required to run hypervisors on x86. > That needs an exported function; there is no way we'll allow random > writes to CR4, there's too much dodgy stuff in there. native_write_cr4 and pv_ops (through which you can do write_cr4) are both exported, and so is cpu_tlbstate which is used by __cr4_set_bits and friends. Am I missing something glaringly obvious? Paolo