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

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Message-ID: <20180417202417.GA29865@localhost.localdomain>
Date:   Tue, 17 Apr 2018 17:24:17 -0300
From:   Eduardo Habkost <ehabkost@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        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 Tue, Apr 17, 2018 at 06:40:58PM +0800, Wanpeng Li wrote:
> 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?

QEMU setting ucode_rev automatically using the host value when
using "-cpu host" (with no need for explicit ucode_rev option)
makes sense to me.

-- 
Eduardo