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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id b18sm9024900ejb.77.2021.03.16.01.16.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Mar 2021 01:16:50 -0700 (PDT) Subject: Re: [PATCH 2/2] KVM: nSVM: improve SYSENTER emulation on AMD To: Maxim Levitsky , kvm@vger.kernel.org Cc: "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "H. Peter Anvin" , Sean Christopherson , Ingo Molnar , Jim Mattson , Vitaly Kuznetsov , Joerg Roedel , Thomas Gleixner , "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Wanpeng Li , Borislav Petkov References: <20210315174316.477511-1-mlevitsk@redhat.com> <20210315174316.477511-3-mlevitsk@redhat.com> <0dbcff57-8197-8fbb-809d-b47a4f5e9e77@redhat.com> <1a4f35e356c50e38916acef6c86175b24efca0a3.camel@redhat.com> From: Paolo Bonzini Message-ID: Date: Tue, 16 Mar 2021 09:16:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <1a4f35e356c50e38916acef6c86175b24efca0a3.camel@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/03/21 19:19, Maxim Levitsky wrote: > On Mon, 2021-03-15 at 18:56 +0100, Paolo Bonzini wrote: >> On 15/03/21 18:43, Maxim Levitsky wrote: >>> + if (!guest_cpuid_is_intel(vcpu)) { >>> + /* >>> + * If hardware supports Virtual VMLOAD VMSAVE then enable it >>> + * in VMCB and clear intercepts to avoid #VMEXIT. >>> + */ >>> + if (vls) { >>> + svm_clr_intercept(svm, INTERCEPT_VMLOAD); >>> + svm_clr_intercept(svm, INTERCEPT_VMSAVE); >>> + svm->vmcb->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK; >>> + } >>> + /* No need to intercept these msrs either */ >>> + set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 1, 1); >>> + set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 1, 1); >>> + } >> >> An "else" is needed here to do the opposite setup (removing the "if >> (vls)" from init_vmcb). > > init_vmcb currently set the INTERCEPT_VMLOAD and INTERCEPT_VMSAVE and it doesn't enable vls There's also this towards the end of the function: /* * If hardware supports Virtual VMLOAD VMSAVE then enable it * in VMCB and clear intercepts to avoid #VMEXIT. */ if (vls) { svm_clr_intercept(svm, INTERCEPT_VMLOAD); svm_clr_intercept(svm, INTERCEPT_VMSAVE); svm->vmcb->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK; } > thus there is nothing to do if I don't want to enable vls. > It seems reasonable to me. > > Both msrs I marked as '.always = false' in the > 'direct_access_msrs', which makes them be intercepted by the default. > If I were to use '.always = true' it would feel a bit wrong as the intercept is not always > enabled. I agree that .always = false is correct. > What do you think? You can set the CPUID multiple times, so you could go from AMD to Intel and back. Thanks, Paolo