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

[David Woodhouse]

On Fri, 2026-03-27 at 04:05 +0100, Ahmed S. Darwish wrote:
> Hi,
> 
> I'm happy to announce release 3.0 of the x86-cpuid-db project:
> 
>    https://gitlab.com/x86-cpuid.org/x86-cpuid-db
>    https://gitlab.com/x86-cpuid.org/x86-cpuid-db/-/releases/v3.0

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/

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