Re: [PATCH v2 5/8] x86/pv: allow reading FEATURE_CONTROL MSR

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.08.2020 17:08, Roger Pau Monne wrote:
> @@ -181,6 +182,18 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t 
> *val)
>          /* Not offered to guests. */
>          goto gp_fault;
>  
> +    case MSR_IA32_FEATURE_CONTROL:
> +        if ( !(cp->x86_vendor & X86_VENDOR_INTEL) )
> +            goto gp_fault;

Can we really do it this way round, rather than raising #GP when
we know the MSR isn't there (AMD / Hygon)? I realized code e.g.
...

> +        *val = IA32_FEATURE_CONTROL_LOCK;
> +        if ( vmce_has_lmce(v) )
> +            *val |= IA32_FEATURE_CONTROL_LMCE_ON;
> +        if ( nestedhvm_enabled(d) )
> +            *val |= IA32_FEATURE_CONTROL_ENABLE_VMXON_OUTSIDE_SMX;
> +        break;
> +
> +
>      case MSR_IA32_PLATFORM_ID:
>          if ( !(cp->x86_vendor & X86_VENDOR_INTEL) ||
>               !(boot_cpu_data.x86_vendor & X86_VENDOR_INTEL) )

... in context right here does it the same way, but I still
wonder whether we wouldn't better switch existing instances, too.

Jan