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

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Message-ID: <1d40dca9-c128-0390-98d2-5ca9c8791448@redhat.com>
Date:   Tue, 31 Jul 2018 14:59:06 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     whiteheadm@....org
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: kvm: Restrict X86_FEATURE_VMMCALL to x86_64 platform

On 31/07/2018 14:57, tedheadster wrote:
>>
>> 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.

It's a bit silly, but it's not particularly wrong.

Paolo