linux-kernel - Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

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Date:   Mon, 26 Feb 2018 19:25:28 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

2018-02-26 19:16 GMT+08:00 Borislav Petkov <bp@...en8.de>:
> On Mon, Feb 26, 2018 at 07:02:29PM +0800, Wanpeng Li wrote:
>> > So a guest will have *two* microcode revisions - both of which are most
>> > likely wrong?!
>>
>> Just one revision.
>
> So what does "the non-sensical value which is written by the guest will
> not reflect to guest-visible microcode revision" even mean then?
>
> cat /proc/cpuinfo
>
> in the guest shows what exactly?
>
> And what would RDMSR 0x8b show then?

Both are the same values set by kvm userspace.

>
>> https://lkml.org/lkml/2017/12/9/29 The original discussion explain in
>> more details.
>

> approach. Instead, the kernel should not look at microcode revisions if
> it runs virtualized.

This is correct. The link explains why the userspace sets microcode
revision is still needed.

Regards,
Wanpeng Li