Re: [Xen-devel] [PATCH 17/19] x86/vmce, tools/libxl: expose LMCE capability in guest MSR_IA32_MCG_CAP

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.02.17 at 07:39, <haozhong.zhang@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/cpu/mcheck/vmce.c
> +++ b/xen/arch/x86/cpu/mcheck/vmce.c
> @@ -74,7 +74,7 @@ int vmce_restore_vcpu(struct vcpu *v, const struct 
> hvm_vmce_vcpu *ctxt)
>      unsigned long guest_mcg_cap;
>  
>      if ( boot_cpu_data.x86_vendor == X86_VENDOR_INTEL )
> -        guest_mcg_cap = INTEL_GUEST_MCG_CAP;
> +        guest_mcg_cap = INTEL_GUEST_MCG_CAP | (lmce_support ? MCG_LMCE_P : 
> 0);
>      else
>          guest_mcg_cap = AMD_GUEST_MCG_CAP;
>  

Is it really a problem to restore a guest that has LMCE enabled on
an LMCE-incapable host? I.e. doesn't the guest need to be aware
of MCEs with the local bit clear anyway?

> @@ -4185,6 +4186,12 @@ static int hvmop_set_param(
>          }
>          d->arch.x87_fip_width = a.value;
>          break;
> +    case HVM_PARAM_LMCE:
> +        if ( a.value > 1 )
> +            rc = -EINVAL;
> +        else if ( a.value == 1 )
> +            rc = vmce_enable_lmce(d);
> +        break;

If you named the param slightly differently, and if you introduced
a #define for the one bit you care about, it could be ready for use
for further future flags right away.

Jan


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