Re: [PATCH v3 08/13] libs/guest: make a cpu policy compatible with older Xen versions

[Jan Beulich <jbeulich@xxxxxxxx>]

On 30.04.2021 17:52, Roger Pau Monne wrote:
> @@ -1086,3 +1075,42 @@ int xc_cpu_policy_calc_compatible(xc_interface *xch,
>  
>      return rc;
>  }
> +
> +int xc_cpu_policy_make_compatible(xc_interface *xch, xc_cpu_policy_t policy,
> +                                  bool hvm)

I'm concerned of the naming, and in particular the two very different
meanings of "compatible" for xc_cpu_policy_calc_compatible() and this
new one. I'm afraid I don't have a good suggestion though, short of
making the name even longer and inserting "backwards".

Jan

> +{
> +    xc_cpu_policy_t host;
> +    int rc;
> +
> +    host = xc_cpu_policy_init();
> +    if ( !host )
> +    {
> +        errno = ENOMEM;
> +        return -1;
> +    }
> +
> +    rc = xc_cpu_policy_get_system(xch, XEN_SYSCTL_cpu_policy_host, host);
> +    if ( rc )
> +    {
> +        ERROR("Failed to get host policy");
> +        goto out;
> +    }
> +
> +    /*
> +     * Account for features which have been disabled by default since Xen 
> 4.13,
> +     * so migrated-in VM's don't risk seeing features disappearing.
> +     */
> +    policy->cpuid.basic.rdrand = host->cpuid.basic.rdrand;
> +
> +    if ( hvm )
> +        policy->cpuid.feat.mpx = host->cpuid.feat.mpx;
> +
> +    /* Clamp maximum leaves to the ones supported on 4.12. */
> +    policy->cpuid.basic.max_leaf = min(policy->cpuid.basic.max_leaf, 0xdu);
> +    policy->cpuid.feat.max_subleaf = 0;
> +    policy->cpuid.extd.max_leaf = min(policy->cpuid.extd.max_leaf, 0x1cu);
> +
> + out:
> +    xc_cpu_policy_destroy(host);
> +    return rc;
> +}
>