Re: [PATCH 08/13] libs/guest: introduce support for setting guest MSRs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.06.2023 15:10, Roger Pau Monne wrote:
> --- a/tools/libs/guest/xg_cpuid_x86.c
> +++ b/tools/libs/guest/xg_cpuid_x86.c
> @@ -331,10 +331,74 @@ int xc_cpu_policy_apply_cpuid(xc_interface *xch, 
> xc_cpu_policy_t *policy,
>      return 0;
>  }
>  
> +int xc_cpu_policy_apply_msr(xc_interface *xch, xc_cpu_policy_t *policy,
> +                            const struct xc_msr *msr,
> +                            const xc_cpu_policy_t *host)
> +{
> +    for ( ; msr->index != XC_MSR_INPUT_UNUSED; ++msr )
> +    {
> +        xen_msr_entry_t cur_msr, host_msr;
> +        int rc;
> +
> +        rc = xc_cpu_policy_get_msr(xch, policy, msr->index, &cur_msr);
> +        if ( rc )
> +        {
> +            ERROR("Failed to get current MSR %#x", msr->index);
> +            return rc;
> +        }
> +        rc = xc_cpu_policy_get_msr(xch, host, msr->index, &host_msr);
> +        if ( rc )
> +        {
> +            ERROR("Failed to get host policy MSR %#x", msr->index);
> +            return rc;
> +        }
> +
> +        for ( unsigned int i = 0; i < ARRAY_SIZE(msr->policy) - 1; i++ )

While correct, the "- 1" struck me as odd. Could we deviate a little from
the CPUID side and permit an early nul in the string, implying all 'x' in
subsequent slots? Then you could drop the -1 here and simply bail from the
loop when finding a nul char.

Jan