On Wed, 2024-05-01 at 16:15 -0700, Sean Christopherson wrote: > On Sun, Feb 18, 2024, Yang Weijiang wrote: > > @@ -696,6 +697,20 @@ void kvm_set_cpu_caps(void) > > kvm_cpu_cap_set(X86_FEATURE_INTEL_STIBP); > > if (boot_cpu_has(X86_FEATURE_AMD_SSBD)) > > kvm_cpu_cap_set(X86_FEATURE_SPEC_CTRL_SSBD); > > + /* > > + * Don't use boot_cpu_has() to check availability of IBT because the > > + * feature bit is cleared in boot_cpu_data when ibt=off is applied > > + * in host cmdline. > > I'm not convinced this is a good reason to diverge from the host kernel. E.g. > PCID and many other features honor the host setup, I don't see what makes IBT > special. > > LA57 is special because it's entirely reasonable, likely even, for a host to > only want to use 48-bit virtual addresses, but still want to let the guest > enable > LA57. Definitely. I swear we (Weijiang and I) had a back and forth at some point where we agreed to match the host support. Plus I think the CET FPU stuff triggers off of host support for CET. So if the host doesn't have X86_FEATURE_SHSTK or X86_FEATURE_IBT then... hopefully it's caught later. But then don't report it's supported.
