| Message ID | 20210914154825.104886-7-mlevitsk@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | nSVM fixes and optional features | expand |
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@redhat.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
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);
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@redhat.com> --- arch/x86/kvm/svm/svm.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)