linux-kernel - Re: [RFC PATCH v3] tools/x86: add kcpuid tool to show raw CPU features

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Message-ID: <20201119141512.GB3769@zn.tnic>
Date:   Thu, 19 Nov 2020 15:15:12 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, nivedita@...m.mit.edu,
        thomas.lendacky@....com, yazen.ghannam@....com, wei.huang2@....com
Subject: Re: [RFC PATCH v3] tools/x86: add kcpuid tool to show raw CPU
 features

On Thu, Nov 19, 2020 at 09:50:10PM +0800, Feng Tang wrote:
> That's really odd. I tried on 3 baremetal machines: one Skylake NUC device,
> one Xeon E5-2699 and one Xeon E5-2680.

Ah, sorry, not virt, virt is 0x4000_0000. Yeah, I remember now. It is
function 4 which AMD doesn't implement and I'm running this on AMD:

$ cpuid -1r
CPU:
   0x00000000 0x00: eax=0x0000000d ebx=0x68747541 ecx=0x444d4163 edx=0x69746e65
   0x00000001 0x00: eax=0x00800f82 ebx=0x0c100800 ecx=0x7ed8320b edx=0x178bfbff
   0x00000002 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 edx=0x00000000
   0x00000003 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 edx=0x00000000

<-- no function 4.

   0x00000005 0x00: eax=0x00000040 ebx=0x00000040 ecx=0x00000003 edx=0x00000011
   ...

That's why.  :-)

Btw, there are other funny ranges on Intel:

./cpuid -1r
CPU:
   0x20000000 0x00: eax=0x00000000 ebx=0x00000001 ecx=0x00000001 edx=0x00000000

That one has 2 bits set.

   0x80860000 0x00: eax=0x00000000 ebx=0x00000001 ecx=0x00000001 edx=0x00000000
   0xc0000000 0x00: eax=0x00000000 ebx=0x00000001 ecx=0x00000001 edx=0x00000000

And those too.

Fun.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette