linux-kernel - Re: [PATCH v10 18/39] KVM: x86: hyper-v: Introduce fast guest_hv_cpuid_has_l2_tlb

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Date:   Wed, 21 Sep 2022 21:19:06 +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 18/39] KVM: x86: hyper-v: Introduce fast
 guest_hv_cpuid_has_l2_tlb_flush() check

On Wed, Sep 21, 2022, 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.
> 
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/hyperv.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index 1b53dd4cff4d..3fff3a6f4bb9 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -174,6 +174,13 @@ static inline void kvm_hv_vcpu_empty_flush_tlb(struct kvm_vcpu *vcpu)
>  	kfifo_reset_out(&tlb_flush_fifo->entries);
>  }
>  
> +static inline bool guest_hv_cpuid_has_l2_tlb_flush(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> +
> +	return hv_vcpu && (hv_vcpu->cpuid_cache.nested_eax & HV_X64_NESTED_DIRECT_FLUSH);

Nit, IMO this is long enough that it's worth wrapping to fit under the soft char limit.

	return hv_vcpu &&
	       (hv_vcpu->cpuid_cache.nested_eax & HV_X64_NESTED_DIRECT_FLUSH);

> +}
> +
>  static inline bool kvm_hv_is_tlb_flush_hcall(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> -- 
> 2.37.3
>