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

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Message-ID: <CANRm+CyyL2jjjn7nZtLJvP+t1pN9ndAGhijmbX4LJh15=O+dvQ@mail.gmail.com>
Date:   Tue, 17 Apr 2018 18:40:58 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Eduardo Habkost <ehabkost@...hat.com>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

Cc Eduardo,
2018-02-26 20:41 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> On 26/02/2018 13:22, Borislav Petkov wrote:
>> On Mon, Feb 26, 2018 at 01:18:07PM +0100, Paolo Bonzini wrote:
>>>> In this context, "host-initiated" write means written by KVM userspace
>>>> with ioctl(KVM_SET_MSR).  It generally happens only on VM startup, reset
>>>> or live migration.
>>>
>>> To be clear, the target of the write is still the vCPU's emulated MSR.
>>
>> So how am I to imagine this as a user:
>>
>> qemu-system-x86_64 --microcode-revision=0xdeadbeef...
>
> More like "-cpu foo,ucode_rev=0xdeadbeef".  But in practice what would
> happen is one of the following:
>
> 1) "-cpu host" sets ucode_rev to the same value of the host, everyone
> else leaves it to zero as is now.

Hi Paolo,

Do you mean the host admin to get the ucode_rev from the host and set
to -cpu host, ucode_rev=xxxxxx or qemu get the ucode_rev directly by
rdmsr?

Regards,
Wanpeng Li