Re: [PATCH 4/5] x86/cpuid: Standardize on u32 in <asm/cpuid/api.h>

["Ahmed S. Darwish" <darwi@linutronix.de>]

On Tue, 18 Mar 2025, H. Peter Anvin wrote:
>
> tglx has suggested that we should cache or even preload the cpuid data
> (the latter would have the potential advantage of making the memory
> data structures a little easier to manage, given the very large
>  potential space.)
>

This is indeed in the patch queue that I plan to send after this leaf
cleanups one gets merged.  We have a data model and CPUIDs are cached on
early boot.  The cache is also refreshed during machine state changes
where the CPUIDs can change; e.g. a microcode update, PSN disable, etc.

Call sites then just do:

    a = cpudata_cpuid(c, 0x0)->max_std_leaf;
    b = cpudata_cpuid(c, 0x80000000)->max_ext_leaf;

    struct leaf_0x1_0 *l1 = cpudata_cpuid(c, 0x1);
    x = l0->cpu_vendorid_0;
    y = l0->cpu_vendorid_1;
    z = l0->cpu_vendorid_2;

and all the data is retrieved auto-magically from the cached tables.

The struct leaf_0xM_N C99 bitfield listings are auto generated by
x86-cpuid-db of course, just like in tools/arch/x86/kcpuid/cpuid.csv.

Thanks,

--
Ahmed S. Darwish
Linutronix GmbH