On Fri, May 23, 2014 at 04:51:53PM +0200, Paolo Bonzini wrote:
> When Hyper-V enlightenments are in effect, Windows prefers to issue an
> Hyper-V MSR write to issue an EOI rather than an x2apic MSR write.
> The Hyper-V MSR write is not handled by the processor, and besides
> being slower, this also causes bugs with APIC virtualization. The
> reason is that on EOI the processor will modify the highest in-service
> interrupt (SVI) field of the VMCS, as explained in section 29.1.4 of
> the SDM.
>
> We need to do the same, and be careful not to muck with the isr_count
> and highest_isr_cache fields that are unused when virtual interrupt
> delivery is enabled.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
FWIW
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
some questions below.
> ---
> arch/x86/kvm/lapic.c | 62 ++++++++++++++++++++++++++++++++++---------------
> 1 files changed, 43 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 9736529..0069118 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -360,6 +360,8 @@ static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)
>
> static inline void apic_set_isr(int vec, struct kvm_lapic *apic)
> {
> + /* Note that we never get here with APIC virtualization enabled. */
> +
> if (!__apic_test_and_set_vector(vec, apic->regs + APIC_ISR))
> ++apic->isr_count;
> BUG_ON(apic->isr_count > MAX_APIC_VECTOR);
> @@ -371,12 +373,48 @@ static inline void apic_set_isr(int vec, struct kvm_lapic *apic)
> apic->highest_isr_cache = vec;
> }
>
> +static inline int apic_find_highest_isr(struct kvm_lapic *apic)
> +{
> + int result;
> +
> + /*
> + * Note that isr_count is always 1, and highest_isr_cache
> + * is always -1, with APIC virtualization enabled.
> + */
> + if (!apic->isr_count)
> + return -1;
> + if (likely(apic->highest_isr_cache != -1))
> + return apic->highest_isr_cache;
> +
> + result = find_highest_vector(apic->regs + APIC_ISR);
> + ASSERT(result == -1 || result >= 16);
> +
> + return result;
> +}
> +
> static inline void apic_clear_isr(int vec, struct kvm_lapic *apic)
> {
> - if (__apic_test_and_clear_vector(vec, apic->regs + APIC_ISR))
> + struct kvm_vcpu *vcpu;
> + if (!__apic_test_and_clear_vector(vec, apic->regs + APIC_ISR))
> + return;
> +
> + vcpu = apic->vcpu;
> +
> + /*
> + * We do get here for APIC virtualization enabled if the guest
> + * uses the Hyper-V APIC enlightenment. In this case we may need
> + * to trigger a new interrupt delivery by writing the SVI field;
> + * on the other hand isr_count and highest_isr_cache are unused
> + * and must be left alone.
> + */
> + if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
> + kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
> + apic_find_highest_isr(apic));
I note that an indirect call on data path is mostly unnecessary here:
static int vmx_vm_has_apicv(struct kvm *kvm)
{
return enable_apicv && irqchip_in_kernel(kvm);
}
is all it does, and irqchip_in_kernel also has an rmb within it, which
is somewhat expensive on x86: and there's no way to reach this code
with irqchip disabled, correct?
So this is penalizing non-apicv boxes.
How about adding a bool flag in kvm_vcpu_arch, and testing that?
Or even move the enable_apicv module parameter to x86.
> + else {
> --apic->isr_count;
> - BUG_ON(apic->isr_count < 0);
> - apic->highest_isr_cache = -1;
> + BUG_ON(apic->isr_count < 0);
> + apic->highest_isr_cache = -1;
> + }
> }
>
> int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu)
> @@ -456,22 +494,6 @@ static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu)
> __clear_bit(KVM_APIC_PV_EOI_PENDING, &vcpu->arch.apic_attention);
> }
>
> -static inline int apic_find_highest_isr(struct kvm_lapic *apic)
> -{
> - int result;
> -
> - /* Note that isr_count is always 1 with vid enabled */
> - if (!apic->isr_count)
> - return -1;
> - if (likely(apic->highest_isr_cache != -1))
> - return apic->highest_isr_cache;
> -
> - result = find_highest_vector(apic->regs + APIC_ISR);
> - ASSERT(result == -1 || result >= 16);
> -
> - return result;
> -}
> -
> void kvm_apic_update_tmr(struct kvm_vcpu *vcpu, u32 *tmr)
> {
> struct kvm_lapic *apic = vcpu->arch.apic;
> @@ -1605,6 +1627,8 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
> int vector = kvm_apic_has_interrupt(vcpu);
> struct kvm_lapic *apic = vcpu->arch.apic;
>
> + /* Note that we never get here with APIC virtualization enabled. */
> +
> if (vector == -1)
> return -1;
>
> --
> 1.7.1
>
> --
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