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Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
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Date:   Fri, 22 Jul 2022 19:22:27 +0200
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Subject: Re: [PATCH v4 01/25] KVM: x86: hyper-v: Expose access to debug MSRs
 in the partition privilege flags
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To:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>
Cc:     kvm@vger.kernel.org,
        Anirudh Rayabharam <anrayabh@linux.microsoft.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20220714091327.1085353-1-vkuznets@redhat.com>
 <20220714091327.1085353-2-vkuznets@redhat.com> <YtnIgQOPbcZOQK2D@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <YtnIgQOPbcZOQK2D@google.com>
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On 7/21/22 23:43, Sean Christopherson wrote:
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index c284a605e453..ca91547034e4 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1282,7 +1282,7 @@ static bool hv_check_msr_access(struct kvm_vcpu_hv *hv_vcpu, u32 msr)
>          case HV_X64_MSR_SYNDBG_OPTIONS:
>          case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
>                  return hv_vcpu->cpuid_cache.features_edx &
> -                       HV_FEATURE_DEBUG_MSRS_AVAILABLE;
> +                       HV_ACCESS_DEBUG_MSRS;
>          default:
>                  break;
>          }
> 

Yes, and this will need some kind of hack in QEMU to expose both CPUID 
bits.  Fortunately hv-syndbg shouldn't be in much use in the wild, so I 
think we can avoid quirks etc.

Paolo