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 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.suthikulpa...@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