Re: [PART1 RFC v3 11/12] svm: Do not intercept CR8 when enable AVIC

[Suravee Suthikulpanit]

Hi Radim,

On 3/19/16 04:10, Radim KrÄmÃÅ wrote:
> 2016-03-18 01:09-0500, Suravee Suthikulpanit:
> > When enable AVIC:
> >      * Do not intercept CR8 since this should be handled by AVIC HW.
> >      * Also update TPR in APIC backing page when syncing CR8 before VMRUN
> >
> > Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> > ---
> >   arch/x86/kvm/svm.c | 15 +++++++++++----
> >   1 file changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index ba84d57..d5418c3 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -984,6 +984,8 @@ static __init int svm_hardware_setup(void)
> >
> >   	if (avic) {
> >   		printk(KERN_INFO "kvm: AVIC enabled\n");
> > +
> > +		svm_x86_ops.update_cr8_intercept = NULL;
>
> This doesn't look right.

Actually, I don't think this change isn't necessary since we don't even 
call kvm_x86_ops->update_cr8_intercept() if vcpu->arch.apicv_active (See 
arch/x86/kvm/x86.c: update_cr8_intercept()).

> [....]
> > @@ -4080,7 +4083,8 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
> >   {
> >   	struct vcpu_svm *svm = to_svm(vcpu);
> >
> > -	if (is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK))
> > +	if ((is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK)) ||
> > +	     svm_vcpu_avic_enabled(svm))
> >   		return;
> >
> >   	clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
> > @@ -4271,9 +4275,12 @@ static inline void sync_lapic_to_cr8(struct kvm_vcpu *vcpu)
> >   	if (is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK))
> >   		return;
>
> I think we can exit early with svm_vcpu_avic_enabled().

Right.

> > -	cr8 = kvm_get_cr8(vcpu);
> > +	cr8 = kvm_get_cr8(vcpu) & V_TPR_MASK;
> >   	svm->vmcb->control.int_ctl &= ~V_TPR_MASK;
> > -	svm->vmcb->control.int_ctl |= cr8 & V_TPR_MASK;
> > +	svm->vmcb->control.int_ctl |= cr8;
> > +
> > +	if (svm_vcpu_avic_enabled(svm))
> > +		kvm_lapic_set_reg(svm->vcpu.arch.apic, APIC_TASKPRI, (u32)cr8 << 4);
>
> kvm_get_cr8() == kvm_lapic_get_reg(APIC_TASKPRI) >> 4.

Good point. I'll clean up and simplify this function.

Thanks,
Suravee