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

Suravee Suthikulpanit
2016-03-30T12:15:48Z

Hi Radim,

On 3/19/16 04:10, Radim Krčmář 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@amd.com>
>> ---
>> 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