linux-kernel - Re: [PATCH v10 02/39] KVM: x86: hyper-v: Resurrect dedicated KVM_REQ_HV_TLB

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Message-ID: <Yys6b1ZqYbw9Umyu@google.com>
Date:   Wed, 21 Sep 2022 16:23:11 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 02/39] KVM: x86: hyper-v: Resurrect dedicated
 KVM_REQ_HV_TLB_FLUSH flag

On Wed, Sep 21, 2022, Vitaly Kuznetsov wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f62d5799fcd7..86504a8bfd9a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3418,11 +3418,17 @@ static inline void kvm_vcpu_flush_tlb_current(struct kvm_vcpu *vcpu)
>   */
>  void kvm_service_local_tlb_flush_requests(struct kvm_vcpu *vcpu)
>  {
> -	if (kvm_check_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu))
> +	if (kvm_check_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu)) {
>  		kvm_vcpu_flush_tlb_current(vcpu);
> +		kvm_clear_request(KVM_REQ_HV_TLB_FLUSH, vcpu);

This isn't correct, flush_tlb_current() flushes "host" TLB entries, i.e. guest-physical
mappings in Intel terminology, where flush_tlb_guest() and (IIUC) Hyper-V's paravirt
TLB flush both flesh "guest" TLB entries, i.e. linear and combined mappings.

Amusing side topic, apparently I like arm's stage-2 terminology better than "TDP",
because I actually typed out "stage-2" first.

> +	}
>  
> -	if (kvm_check_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu))
> +	if (kvm_check_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu)) {
> +		kvm_vcpu_flush_tlb_guest(vcpu);
> +		kvm_clear_request(KVM_REQ_HV_TLB_FLUSH, vcpu);
> +	} else if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu)) {
>  		kvm_vcpu_flush_tlb_guest(vcpu);
> +	}
>  }
>  EXPORT_SYMBOL_GPL(kvm_service_local_tlb_flush_requests);
>  
> -- 
> 2.37.3
>