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

[Konrad Rzeszutek Wilk]

On Mon, Feb 26, 2018 at 01:41:38PM +0100, Paolo Bonzini wrote:
> 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.

0x1 you mean.
> 
> 2) Only Amazon uses this feature and we ignore it. :)

And every other vendor.

Perhaps both ideas should be done? The one Boris suggested (See below, not
compile tested yet), and also this one? Keep in mind that other hypervisor
offerings (say Xen, VMWare, etc) may have provided the correct microcode
or not and it would be good for the OS to be comfortable running under them.