quoted

Considering KVM/virtualization for a CPU that has X86_FEATURE_PSFD
but no other existing feature with MSR_IA32_SPEC_CTRL, if a host
doesn't enable PSFD with the new parameter, the host doesn't have
X86_FEATURE_MSR_SPEC_CTRL.  Then, it would be a problem if its
guests want to use PSFD looking at x86_virt_spec_ctrl().
(I'm not sure how you will change your previous KVM patch though)

Reiji, you are correct that X86_FEATURE_MSR_SPEC_CTRL should be enabled so KVM guests can use PSFD
even if host does not use it.
I have this change in my KVM patch.

Thank you for the response. Yes, that sounds good.

Thanks,
Reiji