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Date: Thu, 23 Sep 2021 18:40:51 +0200 From: Paolo Bonzini <pbonzini@...hat.com> To: Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org Cc: Vitaly Kuznetsov <vkuznets@...hat.com>, Borislav Petkov <bp@...en8.de>, Bandan Das <bsd@...hat.com>, open list <linux-kernel@...r.kernel.org>, Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>, Wei Huang <wei.huang2@....com>, Sean Christopherson <seanjc@...gle.com>, "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>, Jim Mattson <jmattson@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, Shuah Khan <shuah@...nel.org>, Wanpeng Li <wanpengli@...cent.com> Subject: Re: [PATCH 06/14] KVM: x86: SVM: don't set VMLOAD/VMSAVE intercepts on vCPU reset 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 <mlevitsk@...hat.com> > --- > 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
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