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

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Date:   Mon, 26 Feb 2018 12:54:52 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>, Wanpeng Li <kernellwp@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

On 26/02/2018 12:44, Borislav Petkov wrote:
>> The guest write is ignored as the original kvm implementation before the patch.
>
> That will never work because there's no virtualized microcode loader.
> Which will be a dumb idea anyway.
> 
> Goes to show that dealing with microcode revisions for a guest is the
> wrong approach.

I don't understand how one thing follows from the other.  How are writes
to 0x8B related to having a virtualized microcode loaded (which is a
concept that actually makes no sense at all)?

> So that's basically what I'm saying - fix apic_check_deadline_errata()
> to check whether the kernel runs as a guest.

It has already been fixed for a few months, and fixing it is indeed the
right thing to do independent of this patch.

Paolo