Re: [Xen-devel] [PATCH v2 29/30] tools/libxc: Use featuresets rather than guesswork

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.02.16 at 14:42, <andrew.cooper3@xxxxxxxxxx> wrote:
> @@ -467,11 +420,8 @@ static void xc_cpuid_config_xsave(xc_interface *xch,
>          regs[1] = 512 + 64; /* FP/SSE + XSAVE.HEADER */
>          break;
>      case 1: /* leaf 1 */
> -        regs[0] &= (XSAVEOPT | XSAVEC | XGETBV1 | XSAVES);
> -        if ( !info->hvm )
> -            regs[0] &= ~XSAVES;
> -        regs[2] &= info->xfeature_mask;
> -        regs[3] = 0;
> +        regs[0] = info->featureset[featureword_of(X86_FEATURE_XSAVEOPT)];
> +        regs[1] = regs[2] = regs[3] = 0;
>          break;

This change (to regs[2] handling) reminds me of an apparent issue
in the earlier dependencies patch, which I realized only after having
sent the reply, and then forgot to send another reply for: Shouldn't
features requiring certain XSAVE states depend on that state's
availability instead of just XSAVE? That would make the above use
proper masking for both regs[2] and regs[3] (and also for regs[0]
and regs[3] in the sub-leaf 0 case).

Jan


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