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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id b68sm1919858wme.6.2020.01.23.01.15.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jan 2020 01:15:42 -0800 (PST) From: Vitaly Kuznetsov To: Paolo Bonzini , Sean Christopherson Cc: kvm@vger.kernel.org, Jim Mattson , linux-kernel@vger.kernel.org, Liran Alon , Roman Kagan Subject: Re: [PATCH RFC 2/3] x86/kvm/hyper-v: move VMX controls sanitization out of nested_enable_evmcs() In-Reply-To: References: <20200115171014.56405-1-vkuznets@redhat.com> <20200115171014.56405-3-vkuznets@redhat.com> <6c4bdb57-08fb-2c2d-9234-b7efffeb72ed@redhat.com> <20200122054724.GD18513@linux.intel.com> <9c126d75-225b-3b1b-d97a-bcec1f189e02@redhat.com> <87eevrsf3s.fsf@vitty.brq.redhat.com> <20200122155108.GA7201@linux.intel.com> <87blqvsbcy.fsf@vitty.brq.redhat.com> Date: Thu, 23 Jan 2020 10:15:41 +0100 Message-ID: <87zheer0si.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > On 22/01/20 17:29, Vitaly Kuznetsov wrote: >> Yes, in case we're back to the idea to filter things out in QEMU we can >> do this. What I don't like is that every other userspace which decides >> to enable eVMCS will have to perform the exact same surgery as in case >> it sets allow_unsupported_controls=0 it'll have to know (hardcode) the >> filtering (or KVM_SET_MSRS will fail) and in case it opts for >> allow_unsupported_controls=1 Windows guests just won't boot without the >> filtering. >> >> It seems to be 1:1, eVMCSv1 requires the filter. > > Yes, that's the point. It *is* a hack in KVM, but it is generally > preferrable to have an easier API for userspace, if there's only one way > to do it. > > Though we could be a bit more "surgical" and only remove > SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES---thus minimizing the impact on > non-eVMCS guests. Vitaly, can you prepare a v2 that does that and adds > a huge "hack alert" comment that explains the discussion? Yes, sure. I'd like to do more testing to make sure filtering out SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES is enough for other Hyper-V versions too (who knows how many bugs are there :-) -- Vitaly