* Dave Hansen <[email protected]> wrote:
> +static int xfeature_is_supervisor(int xfeature_nr)
> +{
> + /*
> + * We currently do not suport supervisor states, but if
> + * we did, we could find out like this.
> + *
> + * SDM says: If state component i is a user state component,
> + * ECX[0] return 0; if state component i is a supervisor
> + * state component, ECX[0] returns 1.
> + u32 eax, ebx, ecx, edx;
> + cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx);
> + return !!(ecx & 1);
> + */
> + return 0;
> +}
So if this CPUID is documented to work, why not use it to sanity check things?
I.e. do something like:
u32 eax, ebx, ecx, edx;
cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx);
/* Linux doesn't support supervisor states (yet): */
WARN_ON_ONCE(ecx & 1);
return 0;
That would give us a gentle way to double check our assumptions here.
Thanks,
Ingo
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