2019-05-03 13:41:40

by Suthikulpanit, Suravee

Subject: [PATCH] svm/avic: Do not send AVIC doorbell to self

AVIC doorbell is used to notify a running vCPU that interrupts
has been injected into the vCPU AVIC backing page. Current logic
checks only if a VCPU is running before sending a doorbell.
However, the doorbell is not necessary if the destination
CPU is itself.

Add logic to check currently running CPU before sending doorbell.

Signed-off-by: Suravee Suthikulpanit <[email protected]>
---
arch/x86/kvm/svm.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 122788f..4bbf6fc 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5283,10 +5283,13 @@ static void svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
kvm_lapic_set_irr(vec, vcpu->arch.apic);
smp_mb__after_atomic();

- if (avic_vcpu_is_running(vcpu))
- wrmsrl(SVM_AVIC_DOORBELL,
- kvm_cpu_get_apicid(vcpu->cpu));
- else
+ if (avic_vcpu_is_running(vcpu)) {
+ int cpuid = vcpu->cpu;
+
+ if (cpuid != get_cpu())
+ wrmsrl(SVM_AVIC_DOORBELL, kvm_cpu_get_apicid(cpuid));
+ put_cpu();
+ } else
kvm_vcpu_wake_up(vcpu);
}

--
1.8.3.1

2019-05-07 13:19:22

by Alexander Graf

Subject: Re: [PATCH] svm/avic: Do not send AVIC doorbell to self

On 03.05.19 15:38, Suthikulpanit, Suravee wrote:
> AVIC doorbell is used to notify a running vCPU that interrupts
> has been injected into the vCPU AVIC backing page. Current logic
> checks only if a VCPU is running before sending a doorbell.
> However, the doorbell is not necessary if the destination
> CPU is itself.
>
> Add logic to check currently running CPU before sending doorbell.
>
> Signed-off-by: Suravee Suthikulpanit <[email protected]>

Reviewed-by: Alexander Graf <[email protected]>

> ---
> arch/x86/kvm/svm.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 122788f..4bbf6fc 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5283,10 +5283,13 @@ static void svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
> kvm_lapic_set_irr(vec, vcpu->arch.apic);
> smp_mb__after_atomic();
>
> - if (avic_vcpu_is_running(vcpu))
> - wrmsrl(SVM_AVIC_DOORBELL,
> - kvm_cpu_get_apicid(vcpu->cpu));
> - else
> + if (avic_vcpu_is_running(vcpu)) { > + int cpuid = vcpu->cpu;
> +
> + if (cpuid != get_cpu())

Tiny nitpick: What would keep you from checking vcpu->cpu directly here?

Alex

> + wrmsrl(SVM_AVIC_DOORBELL, kvm_cpu_get_apicid(cpuid));
> + put_cpu();
> + } else
> kvm_vcpu_wake_up(vcpu);
> }
>
>

2019-05-14 15:54:55

by Suthikulpanit, Suravee

Subject: Re: [PATCH] svm/avic: Do not send AVIC doorbell to self

Alex,

On 5/7/2019 8:16 AM, Graf, Alexander wrote:
> [CAUTION: External Email]
>
> On 03.05.19 15:38, Suthikulpanit, Suravee wrote:
>> AVIC doorbell is used to notify a running vCPU that interrupts
>> has been injected into the vCPU AVIC backing page. Current logic
>> checks only if a VCPU is running before sending a doorbell.
>> However, the doorbell is not necessary if the destination
>> CPU is itself.
>>
>> Add logic to check currently running CPU before sending doorbell.
>>
>> Signed-off-by: Suravee Suthikulpanit <[email protected]>
>
> Reviewed-by: Alexander Graf <[email protected]>

Thanks.

>> ---
>>   arch/x86/kvm/svm.c | 11 +++++++----
>>   1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 122788f..4bbf6fc 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -5283,10 +5283,13 @@ static void svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
>>       kvm_lapic_set_irr(vec, vcpu->arch.apic);
>>       smp_mb__after_atomic();
>>
>> -     if (avic_vcpu_is_running(vcpu))
>> -             wrmsrl(SVM_AVIC_DOORBELL,
>> -                    kvm_cpu_get_apicid(vcpu->cpu));
>> -     else
>> +     if (avic_vcpu_is_running(vcpu)) { > +           int cpuid = vcpu->cpu;
>> +
>> +             if (cpuid != get_cpu())
>
> Tiny nitpick: What would keep you from checking vcpu->cpu directly here?

Nothing. Just coding style.

Thanks,
Suravee

2019-05-20 17:58:51

by Paolo Bonzini

Subject: Re: [PATCH] svm/avic: Do not send AVIC doorbell to self

On 03/05/19 15:38, Suthikulpanit, Suravee wrote:
> AVIC doorbell is used to notify a running vCPU that interrupts
> has been injected into the vCPU AVIC backing page. Current logic
> checks only if a VCPU is running before sending a doorbell.
> However, the doorbell is not necessary if the destination
> CPU is itself.
>
> Add logic to check currently running CPU before sending doorbell.
>
> Signed-off-by: Suravee Suthikulpanit <[email protected]>
> ---
> arch/x86/kvm/svm.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 122788f..4bbf6fc 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5283,10 +5283,13 @@ static void svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
> kvm_lapic_set_irr(vec, vcpu->arch.apic);
> smp_mb__after_atomic();
>
> - if (avic_vcpu_is_running(vcpu))
> - wrmsrl(SVM_AVIC_DOORBELL,
> - kvm_cpu_get_apicid(vcpu->cpu));
> - else
> + if (avic_vcpu_is_running(vcpu)) {
> + int cpuid = vcpu->cpu;
> +
> + if (cpuid != get_cpu())
> + wrmsrl(SVM_AVIC_DOORBELL, kvm_cpu_get_apicid(cpuid));
> + put_cpu();
> + } else
> kvm_vcpu_wake_up(vcpu);
> }
>
>

Queued, thanks.

Paolo