Re: [PATCH v6 3/3] KVM: selftests: Add self IPI HLT test

Sean Christopherson
2025-02-26T00:38:18Z

On Tue, Jan 28, 2025, Manali Shukla wrote:
> + if (kvm_cpu_has(X86_FEATURE_IDLE_HLT))

Well, shoot. I gave you bad input, and we're stuck.

this_cpu_has() isn't correct, because the part of my previous feedback about
needing to check *KVM* support was 100% correct. But kvm_cpu_has() isn't right
either, because that checks what KVM supports exposing to the guest, not what
KVM itself supports/uses. E.g. even if we add full nested support, the test would
fail if nested=0 due to KVM not "supporting" Idle HLT despite using it under the
hood.

The lack of a way for KVM to communicate support to the user has come up in the
past, e.g. in discussion around /proc/cpuinfo. Sadly, AFAIK there are no (good)
ideas on what that should look like.

For now, I'll just skip this patch, even though doing so makes me quite sad.