linux-kernel - Re: [PATCH v2 2/2] x86/kvm/hyper-v: recommend using eVMCS only when it is enabled

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Message-ID: <87h8dxnesa.fsf@vitty.brq.redhat.com>
Date:   Fri, 25 Jan 2019 12:43:33 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Liran Alon <liran.alon@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] x86/kvm/hyper-v: recommend using eVMCS only when it is enabled

Vitaly Kuznetsov <vkuznets@...hat.com> writes:

> We shouldn't probably be suggesting using Enlightened VMCS when it's not
> enabled (not supported from guest's point of view). Hyper-V on KVM seems
> to be fine either way but let's be consistent.
>

Fixes: 2bc39970e932 ("x86/kvm/hyper-v: Introduce KVM_GET_SUPPORTED_HV_CPUID")

is missing here. Hope it can be added upon commit.

> Reviewed-by: Liran Alon <liran.alon@...cle.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/hyperv.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 4840f5b3c88f..4730fcaa70cf 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1850,7 +1850,8 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>  			ent->eax |= HV_X64_RELAXED_TIMING_RECOMMENDED;
>  			ent->eax |= HV_X64_CLUSTER_IPI_RECOMMENDED;
>  			ent->eax |= HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED;
> -			ent->eax |= HV_X64_ENLIGHTENED_VMCS_RECOMMENDED;
> +			if (evmcs_ver)
> +				ent->eax |= HV_X64_ENLIGHTENED_VMCS_RECOMMENDED;
>  
>  			/*
>  			 * Default number of spinlock retry attempts, matches

-- 
Vitaly