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

[Sean Christopherson <seanjc@xxxxxxxxxx>]

On Thu, Jul 14, 2022, Vitaly Kuznetsov wrote:
> For some features, Hyper-V spec defines two separate CPUID bits: one
> listing whether the feature is supported or not and another one showing
> whether guest partition was granted access to the feature ("partition
> privilege mask"). 'Debug MSRs available' is one of such features. Add
> the missing 'access' bit.
> 
> Fixes: f97f5a56f597 ("x86/kvm/hyper-v: Add support for synthetic debugger interface")
> Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>  arch/x86/kvm/hyperv.c             | 1 +
>  include/asm-generic/hyperv-tlfs.h | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index e2e95a6fccfd..e08189211d9a 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -2496,6 +2496,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>  			ent->eax |= HV_MSR_RESET_AVAILABLE;
>  			ent->eax |= HV_MSR_REFERENCE_TSC_AVAILABLE;
>  			ent->eax |= HV_ACCESS_FREQUENCY_MSRS;
> +			ent->eax |= HV_ACCESS_DEBUG_MSRS;
>  			ent->eax |= HV_ACCESS_REENLIGHTENMENT;

Doesn't KVM also need to switch to enforcing the "access" flag?

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;
        }