linux-kernel - Re: [PATCH] x86: kvm: Restrict X86_FEATURE_VMMCALL to x86

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Message-ID: <CAP8WD_aP5-bh=+NrJV8a3BCMbQK_PyJD88PGRuU8Qh_exFBy9w@mail.gmail.com>
Date:   Tue, 31 Jul 2018 08:57:33 -0400
From:   tedheadster <tedheadster@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: kvm: Restrict X86_FEATURE_VMMCALL to x86_64 platform

>
> This shouldn't be necessary; for systems that don't have virtualization
> extensions, the comment explains why setting X86_FEATURE_VMMCALL is safe.
>
> But it is also wrong, because you can run a 32-bit kernel as a guest on
> a 64-bit processor, and then it should set X86_FEATURE_VMMCALL because
> the processor has the vmmcall instruction and not Intel's vmcall.
>

Paolo,
  I'm running this on a bare metal machine (no virtualization) with a
32-bit AMD i486 class cpu. Should the feature be showing up in
/proc/cpuinfo under the 'flags' line? It does on my machine, and it
looked wrong to me.

- Matthew