linux-kernel - Re: [PATCH] KVM: x86: svm: report MSR_IA32_MCG_EXT

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Message-ID: <20181220200630.GC25497@flask>
Date:   Thu, 20 Dec 2018 21:06:30 +0100
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Joerg Roedel <joro@...tes.org>, x86@...nel.org
Subject: Re: [PATCH] KVM: x86: svm: report MSR_IA32_MCG_EXT_CTL as unsupported

2018-12-19 12:06+0100, Vitaly Kuznetsov:
> AMD doesn't seem to implement MSR_IA32_MCG_EXT_CTL and svm code in kvm
> knows nothing about it, however, this MSR is among emulated_msrs and
> thus returned with KVM_GET_MSR_INDEX_LIST. The consequent KVM_GET_MSRS,
> of course, fails.
> 
> Report the MSR as unsupported to not confuse userspace.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/svm.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 2acb42b74a51..dfdf7d0b7f88 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5845,6 +5845,13 @@ static bool svm_cpu_has_accelerated_tpr(void)
>  
>  static bool svm_has_emulated_msr(int index)
>  {
> +	switch (index) {
> +	case MSR_IA32_MCG_EXT_CTL:
> +		return false;
> +	default:
> +		break;

Queued, thanks.

Btw, I would prefer this without the

  default: break;

as I don't think we'll ever add something there.