Re: [PATCH v6 10/90] x86/cpu: Rescan CPUID table after disabling PSN

[H. Peter Anvin]

On May 13, 2026 10:09:32 AM PDT, Borislav Petkov <bp@xxxxxxxxx> wrote:
>On Wed, May 13, 2026 at 06:51:28PM +0200, Borislav Petkov wrote:
>> I guess we need to know which leaf changes when a MSR bit is toggled and
>> rescan only that leaf alone.
>
>And looking at the current code there:
>
>        /* Disabling the serial number may affect the cpuid level */
>        c->cpuid_level = cpuid_eax(0);
>
>So why do you need to rescan leafs at all?
>
>We don't have to do them now...
>

Not to mention that the only change this *specific* leaf could cause is a change from 2 to 1. The only reason it matters at all is that the number of leaves is reported in /proc/cpuinfo for purely historical reasons (it is completely useless information since parsing CPUID these days requires a lot more than that piece of information.)