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

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Message-ID: <20180226111630.GB4377@pd.tnic>
Date:   Mon, 26 Feb 2018 12:16:30 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Wanpeng Li <kernellwp@...il.com>
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

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?

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

My argument stands: exposing microcode revisions to guests is the wrong
approach. Instead, the kernel should not look at microcode revisions if
it runs virtualized.

-- 
Regards/Gruss,
    Boris.

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