linux-kernel - Re: [RFC PATCH 13/13] KVM: SVM: Use fastpath x2apic IPI emulation when #vmexit with x2AVIC

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Date:   Mon, 7 Mar 2022 13:24:15 +0700
From:   "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, seanjc@...gle.com, joro@...tes.org,
        jon.grimm@....com, wei.huang2@....com, terry.bowman@....com
Subject: Re: [RFC PATCH 13/13] KVM: SVM: Use fastpath x2apic IPI emulation
 when #vmexit with x2AVIC

Maxim,

On 2/25/2022 3:12 AM, Maxim Levitsky wrote:
> On Sun, 2022-02-20 at 20:19 -0600, Suravee Suthikulpanit wrote:
>> When sends IPI to a halting vCPU, the hardware generates
>> avic_incomplete_ipi #vmexit with the
>> AVIC_IPI_FAILURE_TARGET_NOT_RUNNING reason.
>>
>> For x2AVIC, enable fastpath emulation.
>>
>> Signed-off-by: Suravee Suthikulpanit<suravee.suthikulpanit@....com>
>> ---
>>   arch/x86/kvm/svm/avic.c | 2 ++
>>   arch/x86/kvm/x86.c      | 3 ++-
>>   arch/x86/kvm/x86.h      | 1 +
>>   3 files changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
>> index 874c89f8fd47..758a79ee7f99 100644
>> --- a/arch/x86/kvm/svm/avic.c
>> +++ b/arch/x86/kvm/svm/avic.c
>> @@ -428,6 +428,8 @@ int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu)
>>   		kvm_lapic_reg_write(apic, APIC_ICR, icrl);
>>   		break;
>>   	case AVIC_IPI_FAILURE_TARGET_NOT_RUNNING:
>> +		handle_fastpath_set_x2apic_icr_irqoff(vcpu, svm->vmcb->control.exit_info_1);
> This just doesn't seem right - it sends IPI to the target, while we just need to wake it up.
> avic_kick_target_vcpus already does all of this, and it really should be optimized to avoid
> going over all vcpus as it does currently.

Ah, you are right. I'll remove this patch.

Regards,
Suravee