Re: [Xen-devel] [PATCH 04/10] x86/gen-cpuid: Create max and default variations of INIT_*_FEATURES

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.02.2020 21:22, Andrew Cooper wrote:
> For now, write the same content for both.  Update the users of the
> initialisers to use the new name, and extend xen-cpuid to dump both default
> and max featuresets.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Hypervisor and libxc parts
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> --- a/tools/misc/xen-cpuid.c
> +++ b/tools/misc/xen-cpuid.c
> @@ -283,12 +283,18 @@ static void dump_info(xc_interface *xch, bool detail)
>                        nr_features, "Known", detail);
>      decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_SPECIAL),
>                        nr_features, "Special", detail);
> -    decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_PV),
> -                      nr_features, "PV Mask", detail);
> -    
> decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_HVM_SHADOW),
> -                      nr_features, "HVM Shadow Mask", detail);
> -    decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_HVM_HAP),
> -                      nr_features, "HVM Hap Mask", detail);
> +    decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_PV_MAX),
> +                      nr_features, "PV Max", detail);
> +    decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_PV_DEF),
> +                      nr_features, "PV Default", detail);
> +    
> decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_HVM_SHADOW_MAX),
> +                      nr_features, "HVM Shadow Max", detail);
> +    
> decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_HVM_SHADOW_DEF),
> +                      nr_features, "HVM Shadow Default", detail);
> +    
> decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_HVM_HAP_MAX),
> +                      nr_features, "HVM Hap Max", detail);
> +    
> decode_featureset(xc_get_static_cpu_featuremask(XC_FEATUREMASK_HVM_HAP_DEF),
> +                      nr_features, "HVM Hap Default", detail);

Spotting differences between max and default this way is, I assume,
going to be quite difficult / error prone. Wouldn't it be better to
produce the default set in full, and then list just the extra items
in max? Aiui max is always going to be a superset of def.

Jan

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