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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id kx17sm3255053ejc.51.2021.09.23.09.40.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Sep 2021 09:40:54 -0700 (PDT) Subject: Re: [PATCH 06/14] KVM: x86: SVM: don't set VMLOAD/VMSAVE intercepts on vCPU reset To: Maxim Levitsky , kvm@vger.kernel.org Cc: Vitaly Kuznetsov , Borislav Petkov , Bandan Das , open list , Joerg Roedel , Ingo Molnar , Wei Huang , Sean Christopherson , "open list:KERNEL SELFTEST FRAMEWORK" , "H. Peter Anvin" , Jim Mattson , Thomas Gleixner , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Shuah Khan , Wanpeng Li References: <20210914154825.104886-1-mlevitsk@redhat.com> <20210914154825.104886-7-mlevitsk@redhat.com> From: Paolo Bonzini Message-ID: <7289d070-152b-aece-1302-33e5a461657c@redhat.com> Date: Thu, 23 Sep 2021 18:40:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210914154825.104886-7-mlevitsk@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 14/09/21 17:48, Maxim Levitsky wrote: > commit adc2a23734ac ("KVM: nSVM: improve SYSENTER emulation on AMD"), > made init_vmcb set vmload/vmsave intercepts unconditionally, > and relied on svm_vcpu_after_set_cpuid to clear them when possible. > > However init_vmcb is also called when the vCPU is reset, and it is > not followed by another call to svm_vcpu_after_set_cpuid because > the CPUID is already set. > > This mistake makes the VMSAVE/VMLOAD intercept to be set when > it is not needed, and harms performance of the nested guest. > > Fixes: adc2a23734ac ("KVM: nSVM: improve SYSENTER emulation on AMD") > > Signed-off-by: Maxim Levitsky > --- > arch/x86/kvm/svm/svm.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 6645542df9bd..861ac9f74331 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -1199,8 +1199,6 @@ static void init_vmcb(struct kvm_vcpu *vcpu) > svm_set_intercept(svm, INTERCEPT_SHUTDOWN); > svm_set_intercept(svm, INTERCEPT_VMRUN); > svm_set_intercept(svm, INTERCEPT_VMMCALL); > - svm_set_intercept(svm, INTERCEPT_VMLOAD); > - svm_set_intercept(svm, INTERCEPT_VMSAVE); > svm_set_intercept(svm, INTERCEPT_STGI); > svm_set_intercept(svm, INTERCEPT_CLGI); > svm_set_intercept(svm, INTERCEPT_SKINIT); > @@ -1377,6 +1375,10 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu) > svm->guest_state_loaded = false; > > svm_switch_vmcb(svm, &svm->vmcb01); > + > + svm_set_intercept(svm, INTERCEPT_VMLOAD); > + svm_set_intercept(svm, INTERCEPT_VMSAVE); > + > init_vmcb(vcpu); > > svm_vcpu_init_msrpm(vcpu, svm->msrpm); > This needs to be redone after the latest refactoring of svm_vcpu_reset. I'll send a patch myself. Paolo