linux-kernel - Re: [PATCH 06/10] KVM: x86: Move "flush guest's TLB" logic to separate kvm_x86

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Date:   Fri, 21 Feb 2020 18:31:06 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/10] KVM: x86: Move "flush guest's TLB" logic to
 separate kvm_x86_ops hook

On 21/02/20 14:52, Vitaly Kuznetsov wrote:
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index fbabb2f06273..72f7ca4baa6d 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2675,7 +2675,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
>>  	trace_kvm_pv_tlb_flush(vcpu->vcpu_id,
>>  		st->preempted & KVM_VCPU_FLUSH_TLB);
>>  	if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB)
>> -		kvm_vcpu_flush_tlb(vcpu, false);
>> +		kvm_x86_ops->tlb_flush_guest(vcpu);
>>  
>>  	vcpu->arch.st.preempted = 0;
> There is one additional place in hyperv.c where we do TLB flush on
> behalf of the guest, kvm_hv_flush_tlb(). Currently, it does
> KVM_REQ_TLB_FLUSH (resulting in kvm_x86_ops->tlb_flush()), do we need
> something like KVM_REQ_TLB_FLUSH_GUEST instead?

Yes, that would be better since INVEPT does not flush linear mappings.
So, when EPT and VPID is enabled, KVM_REQ_TLB_FLUSH would not flush the
guest's translations.

Paolo