Re: [Qemu-devel] [PATCH 2/5] i386: Add CPUID bit and feature words for IA32_ARCH_CAPABILITIES MSR

[Eduardo Habkost]

On Fri, Jun 29, 2018 at 01:34:04PM +0200, Paolo Bonzini wrote:
> On 28/06/2018 20:30, Eduardo Habkost wrote:
> >> For migration to work, you need to add new "features" corresponding to
> >> the bits in the MSR, and include them in the Icelake-Server and
> >> Icelake-Client models.  Unfortunately there is no code for this in QEMU
> >> yet, though the API is there in KVM.
> > Will all Icelake VCPUs of a given model have the same value on
> > MSR_IA32_ARCH_CAPABILITIES?
> > 
> > If not, we can't choose a value that will work on all cases, and
> > it will require management software to be smarter and explicitly
> > configure some of the MSR bits on the command-line.
> 
> We can expect that it will change as more vulnerabilities are found and
> more microcode updates are issued.  We should get it right from the
> beginning.

Right.  Also, we probably want to enable arch-capabilities on
CPUID by default whenever possible, even if using an old CPU
model.  I expect Daniel's versioned CPU model proposal to help us
address this.

I'm worried about the soft freeze deadline (next Tuesday),
though.  I wouldn't like Icelake to miss QEMU 3.0 just because we
couldn't decide on a default MSR_IA32_ARCH_CAPABILITIES value in
time.

-- 
Eduardo