Re: [ANNOUNCE] x86-cpuid-db: Release v3.0

[Ahmed S. Darwish]

Hi!

On Fri, 27 Mar 2026, David Woodhouse wrote:
>
> It still doesn't iterate over the hypervisor blocks at 0x4000_0x00 and
> find all of them. Both Xen and KVM will advertise the Hyper-V leaves at
> 0x4000_0000 and then their own get shifted to 0x4000_0100. And now we
> can host HyperV-enlightened Xen guests under KVM, perhaps we could do
> HyperV, then Xen, then KVM at 0x4000_0200?
>
> I was checking to see if it has all the ways to detect the Extended
> Destination ID enlightenment documented in the last page ("Hypervisor
> detection via CPUID") of https://david.woodhou.se/ExtDestId.pdf
>
> I think I see the Xen and KVM bits there, and I guess reporting them
> with different strings in feature.c is kind of OK? The Bhyve and
> Viridian bits are missing.
>
> Also, the leaf at 0x40000010 isn't necessarily VMware-specific; it's
> seen elsewhere too. At least EC2 exposes it under KVM. See thread at
> about https://lore.kernel.org/all/aLDo3F3KKW0MzlcH@xxxxxxxxxx/
>

Yes, it's in the plan.

The priority is to get the CPUID model into the kernel:

  [PATCH v6 00/90] x86: Introduce a centralized CPUID data model
  https://lore.kernel.org/lkml/20260327021645.555257-1-darwi@xxxxxxxxxxxxx

including its newly-introduced X86_FEATURE synthetic and hardware-backed
words routing to the CPUID tables.

Then, convert the remaining call sites invoking CPUID, then begin tackling
the guest code querying leaves at the 0x4000 range.

Thanks,
Ahmed