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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id v21sm4296580wml.5.2021.07.22.23.58.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Jul 2021 23:58:34 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson Cc: kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , Oliver Upton , linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: x86: Check the right feature bit for MSR_KVM_ASYNC_PF_ACK access In-Reply-To: References: <20210722123018.260035-1-vkuznets@redhat.com> Date: Fri, 23 Jul 2021 08:58:33 +0200 Message-ID: <87lf5x7bza.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean Christopherson writes: > On Thu, Jul 22, 2021, Vitaly Kuznetsov wrote: >> MSR_KVM_ASYNC_PF_ACK MSR is part of interrupt based asynchronous page fault >> interface and not the original (deprecated) KVM_FEATURE_ASYNC_PF. This is >> stated in Documentation/virt/kvm/msr.rst. >> >> Fixes: 66570e966dd9 ("kvm: x86: only provide PV features if enabled in guest's CPUID") >> Signed-off-by: Vitaly Kuznetsov >> --- >> arch/x86/kvm/x86.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index d715ae9f9108..88ff7a1af198 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -3406,7 +3406,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) >> return 1; >> break; >> case MSR_KVM_ASYNC_PF_ACK: >> - if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF)) >> + if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF_INT)) > > Do we want to require both, or do we want to let userspace be stupid? > It's OK to be stupid :-) Thinking more about it, I'd suggest we go the other way around: allow access to MSR_KVM_ASYNC_PF_EN when either KVM_FEATURE_ASYNC_PF or KVM_FEATURE_ASYNC_PF_INT are present. This will allow to eventually deprecate KVM_FEATURE_ASYNC_PF completely and switch to KVM_FEATURE_ASYNC_PF_INT exclusively. >> return 1; >> if (data & 0x1) { >> vcpu->arch.apf.pageready_pending = false; >> @@ -3745,7 +3745,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) >> msr_info->data = vcpu->arch.apf.msr_int_val; >> break; >> case MSR_KVM_ASYNC_PF_ACK: >> - if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF)) >> + if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF_INT)) >> return 1; >> >> msr_info->data = 0; >> -- >> 2.31.1 >> > -- Vitaly