linux-kernel - Re: [PATCH v3 17/34] KVM: x86: hyper-v: Introduce fast kvm_hv_l2_tlb_flush

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Date:   Wed, 11 May 2022 14:30:07 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 17/34] KVM: x86: hyper-v: Introduce fast
 kvm_hv_l2_tlb_flush_exposed() check

On Thu, 2022-04-14 at 15:19 +0200, Vitaly Kuznetsov wrote:
> Introduce a helper to quickly check if KVM needs to handle VMCALL/VMMCALL
> from L2 in L0 to process L2 TLB flush requests.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/hyperv.c           | 6 ++++++
>  arch/x86/kvm/hyperv.h           | 7 +++++++
>  3 files changed, 14 insertions(+)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index ce62fde5f4ff..168600490bd1 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -616,6 +616,7 @@ struct kvm_vcpu_hv {
>  		u32 enlightenments_eax; /* HYPERV_CPUID_ENLIGHTMENT_INFO.EAX */
>  		u32 enlightenments_ebx; /* HYPERV_CPUID_ENLIGHTMENT_INFO.EBX */
>  		u32 syndbg_cap_eax; /* HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES.EAX */
> +		u32 nested_features_eax; /* HYPERV_CPUID_NESTED_FEATURES.EAX */
>  	} cpuid_cache;
>  
>  	struct kvm_vcpu_hv_tlb_flush_ring tlb_flush_ring[HV_NR_TLB_FLUSH_RINGS];
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 79aabe0c33ec..68a0df4e3f66 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -2281,6 +2281,12 @@ void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu)
>  		hv_vcpu->cpuid_cache.syndbg_cap_eax = entry->eax;
>  	else
>  		hv_vcpu->cpuid_cache.syndbg_cap_eax = 0;
> +
> +	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_NESTED_FEATURES, 0);
> +	if (entry)
> +		hv_vcpu->cpuid_cache.nested_features_eax = entry->eax;
> +	else
> +		hv_vcpu->cpuid_cache.nested_features_eax = 0;
>  }
>  
>  int kvm_hv_set_enforce_cpuid(struct kvm_vcpu *vcpu, bool enforce)
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index f593c9fd1dee..d8cb6d70dbc8 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -168,6 +168,13 @@ static inline void kvm_hv_vcpu_empty_flush_tlb(struct kvm_vcpu *vcpu)
>  	tlb_flush_ring->read_idx = tlb_flush_ring->write_idx;
>  }
>  
> +static inline bool kvm_hv_l2_tlb_flush_exposed(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> +
> +	return hv_vcpu && (hv_vcpu->cpuid_cache.nested_features_eax & HV_X64_NESTED_DIRECT_FLUSH);
> +}

Tiny nipick (feel free to ignore): maybe use 'supported' instead of 'exposed',
as we don't use this term in KVM often.

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky


> +
>  static inline bool kvm_hv_is_tlb_flush_hcall(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);