linux-kernel - Re: [PATCH v4 01/25] KVM: x86: hyper-v: Expose access to debug MSRs in the partition privilege flags

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Date:   Fri, 22 Jul 2022 19:22:27 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 01/25] KVM: x86: hyper-v: Expose access to debug MSRs
 in the partition privilege flags

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