Re: [PATCH v1 02/26] x86/cpu: Sanitize CPUID(0x80000000) output
"H. Peter Anvin" <[email protected]>
| Newsgroups | dev.linux.lists.x86-cpuid,org.kernel.vger.linux-kernel |
|---|---|
| Message-ID | <[email protected]> |
On May 8, 2025 1:58:11 PM PDT, Andrew Cooper <[email protected]> wrote: >On 08/05/2025 9:40 pm, H. Peter Anvin wrote: >> On May 7, 2025 1:50:48 AM PDT, Andrew Cooper <[email protected]> wrote: >>> On 06/05/2025 6:04 am, Ahmed S. Darwish wrote: >>>> CPUID(0x80000000).EAX returns the max extended CPUID leaf available. On >>>> x86-32 machines >>> How certain are you that it's all 32bit CPUs? AIUI, it's an Intel >>> specific behaviour, not shared by other x86 vendors of the same era. >>> >>> ~Andrew >> All 64-bit machines require CPUID leaf 0x80000000. > >Yes, but why's that relevant? > >What I'm querying is the claim that all 32-bit machines behaved as Intel >did, and returned rubble for out-of-range leaves. > >~Andrew They did not. Non-Intel CPUs did, and do, report 0 for undefined levels. I believe even today Intel CPUs report the "last level" value for up to 0x7fffffff...