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

Eduardo Habkost
2018-04-17T20:24:21Z

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@redhat.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