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([2601:647:4700:9b2:1d50:a6a4:b3be:b3e4]) by smtp.gmail.com with ESMTPSA id n7sm14245864pgm.28.2020.04.07.16.51.55 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 07 Apr 2020 16:51:56 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.80.23.2.2\)) Subject: Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation From: Nadav Amit In-Reply-To: Date: Tue, 7 Apr 2020 16:51:54 -0700 Cc: Peter Zijlstra , 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 Content-Transfer-Encoding: quoted-printable Message-Id: 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> To: Paolo Bonzini X-Mailer: Apple Mail (2.3608.80.23.2.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Apr 7, 2020, at 3:12 PM, Paolo Bonzini wrote: >=20 > 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. >=20 > 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? No, I was the one who missed the obvious thing. Having said that, I still think there are additional cases that need to = be handled. For instance, I see that is_erratum_383() in KVM (AMD) flushes = the local TLB by writing to CR3 the previous value. I am not familiar with = the erratum. Maybe I am missing something again, but I do not see an = appropriate exported alternative in the kernel.