Re: [Xen-devel] [PATCH v2 23/30] xen+tools: Export maximum host and guest cpu featuresets via SYSCTL

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.02.16 at 14:42, <andrew.cooper3@xxxxxxxxxx> wrote:
> @@ -190,6 +191,71 @@ long arch_do_sysctl(
>          }
>          break;
>  
> +    case XEN_SYSCTL_get_cpu_featureset:
> +    {
> +        const uint32_t *featureset;
> +        unsigned int nr;
> +
> +        /* Request for maximum number of features? */
> +        if ( guest_handle_is_null(sysctl->u.cpu_featureset.features) )
> +        {
> +            sysctl->u.cpu_featureset.nr_features = FSCAPINTS;
> +            if ( __copy_field_to_guest(u_sysctl, sysctl,
> +                                       u.cpu_featureset.nr_features) )
> +                ret = -EFAULT;
> +            break;
> +        }
> +
> +        /* Clip the number of entries. */
> +        nr = sysctl->u.cpu_featureset.nr_features;
> +        if ( nr > FSCAPINTS )
> +            nr = FSCAPINTS;

min() (perhaps even allowing to obviate the comment)?

> +        switch ( sysctl->u.cpu_featureset.index )
> +        {
> +        case XEN_SYSCTL_cpu_featureset_raw:
> +            featureset = raw_featureset;
> +            break;
> +
> +        case XEN_SYSCTL_cpu_featureset_host:
> +            featureset = host_featureset;
> +            break;
> +
> +        case XEN_SYSCTL_cpu_featureset_pv:
> +            featureset = pv_featureset;
> +            break;
> +
> +        case XEN_SYSCTL_cpu_featureset_hvm:
> +            featureset = hvm_featureset;
> +            break;
> +
> +        default:
> +            featureset = NULL;
> +            break;
> +        }
> +
> +        /* Bad featureset index? */
> +        if ( !ret && !featureset )
> +            ret = -EINVAL;

Nothing above altered "ret" from its zero value, so the check here
is pointless.

> --- a/xen/include/public/sysctl.h
> +++ b/xen/include/public/sysctl.h
> @@ -766,6 +766,29 @@ struct xen_sysctl_tmem_op {
>  typedef struct xen_sysctl_tmem_op xen_sysctl_tmem_op_t;
>  DEFINE_XEN_GUEST_HANDLE(xen_sysctl_tmem_op_t);
>  
> +/*
> + * XEN_SYSCTL_get_cpu_featureset (x86 specific)
> + *
> + * Return information about the maximum sets of features which can be offered
> + * to different types of guests.  This is all strictly information as found 
> in
> + * `cpuid` feature leaves with no synthetic additions.
> + */

The reference to guests in the comment conflicts with the raw and
host types below.

> +struct xen_sysctl_cpu_featureset {
> +#define XEN_SYSCTL_cpu_featureset_raw      0
> +#define XEN_SYSCTL_cpu_featureset_host     1
> +#define XEN_SYSCTL_cpu_featureset_pv       2
> +#define XEN_SYSCTL_cpu_featureset_hvm      3
> +    uint32_t index;       /* IN: Which featureset to query? */
> +    uint32_t nr_features; /* IN/OUT: Number of entries in/written to
> +                           * 'features', or the maximum number of features if
> +                           * the guest handle is NULL.  NB. All featuresets
> +                           * come from the same numberspace, so have the same
> +                           * maximum length. */
> +    XEN_GUEST_HANDLE_64(uint32) features; /* OUT: */

Stray colon.

Jan


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