Re: [PATCH v7 013/120] x86/cpu: Use parsed CPUID(0x80000000)

[Borislav Petkov]

On Thu, May 28, 2026 at 05:37:35PM +0200, Ahmed S. Darwish wrote:
> At early boot code, use parsed CPUID(0x80000000) instead of invoking a
> direct CPUID query.
> 
> The original code has the check:
> 
>     extended_cpuid_level = ((eax & 0xffff0000) == 0x80000000) ? eax : 0;
> 
> to protect against Intel 32-bit machines without an extended range, where a
> CPUID(0x80000000) query will repeat the output of the max-valid standard
> CPUID leaf output.
> 
> A similar check is already done at the CPUID parser's own CPUID(0x80000000)
> read function:
> 
>     if (CPUID_RANGE(el0->max_ext_leaf) != CPUID_EXT_START) {
>         // Handle error
>     }
> 
> Thus, for the call-site, the parsed CPUID NULL check below:
> 
>     el0 = cpuid_leaf(c, 0x80000000);
>     extended_cpuid_level = el0 ? el0->max_ext_leaf : 0;
> 
> is sufficient.

I don't think this needs the code examples - just explain that the check is
done by the parser now.

Thx.

-- 
Regards/Gruss,
    Boris.

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