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([2001:b07:6468:f312:1cc0:4e4e:f1a9:1745]) by smtp.gmail.com with ESMTPSA id k4sm3429929wrd.72.2020.08.21.02.44.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Aug 2020 02:44:35 -0700 (PDT) Subject: Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is enabled To: Borislav Petkov Cc: Sean Christopherson , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, Dave Hansen , Chang Seok Bae , Peter Zijlstra , Sasha Levin , kvm@vger.kernel.org, Tom Lendacky References: <20200821025050.32573-1-sean.j.christopherson@intel.com> <20200821074743.GB12181@zn.tnic> <3eb94913-662d-5423-21b1-eaf75635142a@redhat.com> <20200821081633.GD12181@zn.tnic> <3b4ba9e9-dbf6-a094-0684-e68248050758@redhat.com> <20200821092237.GF12181@zn.tnic> From: Paolo Bonzini Message-ID: <1442e559-dde4-70f6-85ac-58109cf81c16@redhat.com> Date: Fri, 21 Aug 2020 11:44:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200821092237.GF12181@zn.tnic> 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 21/08/20 11:22, Borislav Petkov wrote: >> Hence the assumption that KVM makes (and has made ever since TSC_AUX was >> introduced. > And *this* is the problem. KVM can't just be grabbing MSRs and claiming > them because it started using them first. You guys need to stop this. If > it is a shared resource, there better be an agreement about sharing it. It's not like we grab MSRs every day. The user-return notifier restores 6 MSRs (7 on very old processors). The last two that were added were MSR_TSC_AUX itself in 2009 (!) and MSR_IA32_TSX_CTRL last year. Paolo