Re: [PATCH v2 14/21] libs/guest: introduce helper to check cpu policy compatibility

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.04.2021 16:01, Roger Pau Monne wrote:
> --- a/tools/libs/guest/xg_cpuid_x86.c
> +++ b/tools/libs/guest/xg_cpuid_x86.c
> @@ -925,3 +925,22 @@ int xc_cpu_policy_update_msrs(xc_interface *xch, 
> xc_cpu_policy_t policy,
>  
>      return rc;
>  }
> +
> +bool xc_cpu_policy_is_compatible(xc_interface *xch, const xc_cpu_policy_t 
> host,
> +                                 const xc_cpu_policy_t guest)
> +{
> +    struct cpu_policy_errors err = INIT_CPU_POLICY_ERRORS;
> +    struct cpu_policy h = { &host->cpuid, &host->msr };
> +    struct cpu_policy g = { &guest->cpuid, &guest->msr };
> +    int rc = x86_cpu_policies_are_compatible(&h, &g, &err);
> +
> +    if ( !rc )
> +        return true;
> +
> +    if ( err.leaf != -1 )
> +        ERROR("Leaf %#x subleaf %#x is not compatible", err.leaf, 
> err.subleaf);
> +    if ( err.msr != -1 )
> +        ERROR("MSR index %#x is not compatible", err.msr);

Personally I'm against making assumptions like these ones about what
(in this case) INIT_CPU_POLICY_ERRORS actually expands to (i.e. three
times -1). I can see how alternatives to this are quickly going to
get ugly, so I'll leave it to others to judge.

Jan