lkml.org 
[lkml]   [2017]   [Sep]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 3/3] KVM: SVM: Add irqchip_split() checks before enabling AVIC
From
Date
Hi Radim,

On 9/8/17 08:53, Radim Krčmář wrote:
> 2017-09-05 22:39-0500, Suravee Suthikulpanit:
>> SVM AVIC hardware accelerates guest write to APIC_EOI register
>> (for edge-trigger interrupt), which means it does not trap to KVM.
>>
>> So, only enable SVM AVIC only in split irqchip mode.
>> (e.g. launching qemu w/ option '-machine kernel_irqchip=split').
>
> Yeah, hacking TMR to get the VM exit could result in future bugs.
> We have to push split irqchip as the deafult in userspaces with this
> change.

Actually, I'm not quite sure about the advantages/disadvantages with split
irqchip, and how it would affect other cases, and why it was not used as default
currently.

>> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
>> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
>> ---
>> arch/x86/kvm/svm.c | 13 +++++++++----
>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index d1b3eb4..7ce191b 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -1292,7 +1291,7 @@ static void init_vmcb(struct vcpu_svm *svm)
>> set_intercept(svm, INTERCEPT_PAUSE);
>> }
>>
>> - if (avic)
>> + if (kvm_vcpu_apicv_active(&svm->vcpu))
>> avic_init_vmcb(svm);
>> /*
>> @@ -1594,6 +1593,12 @@ static int avic_init_vcpu(struct vcpu_svm *svm)
>> if (!avic)
>> return 0;
>>
>> + if (!irqchip_split(svm->vcpu.kvm)) {
>
> The other place used kvm_vcpu_apicv_active() instead of checking
> irqchip_split() directly, so I think it would be better to be consistent
> and do it here too.
> I'd also like if this workaround used !irqchip_split() exactly once.

Ok, I'll clean up in V2.

>> + pr_debug("%s: Disable AVIC due to non-split irqchip.\n",
>> + __func__);
>
> There is going to be too much of those. pr_debug_once() would be a
> better notification. We can also report it in svm_get_enable_apicv().

pr_debug_once does not use dynamic debug APIs. I think I can call pr_debug only
when vcpu_id == 0.

>> + return 0;
>> + }
>> +
>> ret = avic_init_backing_page(&svm->vcpu);
>> if (ret)
>> return ret;
>> @@ -4388,7 +4393,7 @@ static void svm_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set)
>>
>> static bool svm_get_enable_apicv(struct kvm_vcpu *vcpu)
>> {
>> - return avic;
>> + return avic && irqchip_split(vcpu->kvm);
>> }
>>
>> static void svm_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr)
>> @@ -4405,7 +4410,7 @@ static void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
>> struct vcpu_svm *svm = to_svm(vcpu);
>> struct vmcb *vmcb = svm->vmcb;
>>
>> - if (!avic)
>> + if (!avic || !irqchip_split(svm->vcpu.kvm))
>
> Seems like we want !kvm_vcpu_apicv_active() here too.

Right.

>
>> return;
>>
>> vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
>
> (separate bug: refresh should be able to enable avic as well.)
>
> thanks.
>

Thanks,
Suravee

\
 
 \ /
  Last update: 2017-09-12 11:01    [W:0.055 / U:4.980 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site