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

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Message-ID: <CANRm+CwD4GE_tunwAoarq_W_gfomwXQB+ay8YE5KxJCBktDkyw@mail.gmail.com>
Date:   Mon, 26 Feb 2018 19:52:36 +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 19:44 GMT+08:00 Borislav Petkov <bp@...en8.de>:
> On Mon, Feb 26, 2018 at 07:37:32PM +0800, Wanpeng Li 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.
>
>> Hmm, the apic_check_deadline_errata() example can be referred to.
>
> So that's basically what I'm saying - fix apic_check_deadline_errata()
> to check whether the kernel runs as a guest.

Both I and the link agree with your opinion. However, it is hard to
fix all the guest images which have already been used by customers in
cloud environment, anyway, this patch supplies an alternative way to
work around by host admin.

Regards,
Wanpeng Li