Re: [PATCH 1/3] x86/cpufeatures: Add support for cpuid leaf 80000021/EAX (FeatureExt2Eax)

[Kim Phillips]

On 11/4/22 4:48 PM, Borislav Petkov wrote:
> On Fri, Nov 04, 2022 at 04:36:49PM -0500, Kim Phillips wrote:
> > AMD Zen4 processors advertise features in this leaf.
> > Add the leaf and its Automatic IBRS feature bit.
> >
> > Note: New whole leaf (vs a bit) due to propagation via KVM
> > later in this series.
>
> No, not a separate leaf - use scattered.c
>  > For an example what to do for KVM, see
>
> https://lore.kernel.org/r/20221103025030.78371-1-jiaxi.chen@xxxxxxxxxxxxxxx

That adds features that are mutually exclusive between
kvm and the host kernel, unlike AUTOIBRS.

When trying to wire up a scattered host AUTOIBRS version up to
kvm, I couldn't get past all the reverse_cpuid_check()
BUILD_BUGs demanding exclusivity between h/w and "Linux"
(s/w) FEATUREs.

Is there an example of a scattered feature that gets both its
boot_cpu_has() and guest_cpuid_has() satisfied in the same build?

If not, I'll resubmit like this original submission - AUTOIBRS in
a separate h/w leaf.

Thanks,

Kim