On Tue, Jan 12, 2021 at 09:15:52AM -0800, Sean Christopherson wrote:
> We want the boot_cpu_data.x86_capability memcpy() so that KVM doesn't advertise
> support for features that are intentionally disabled in the kernel, e.g. via
> kernel params. Except for a few special cases, e.g. LA57, KVM doesn't enable
> features in the guest if they're disabled in the host, even if the features are
> supported in hardware.
>
> For some features, e.g. SMEP and SMAP, honoring boot_cpu_data is mostly about
> respecting the kernel's wishes, i.e. barring hardware bugs, enabling such
> features in the guest won't break anything. But for other features, e.g. XSAVE
> based features, enabling them in the guest without proper support in the host
> will corrupt guest and/or host state.
Ah ok, that is an important point.
> So it's really the CPUID read that is (mostly) superfluous.
Yeah, but that is cheap, as we established.
Ok then, I don't see anything that might be a problem and I guess we can
try that handling of scattered bits in kvm and see how far we'll get.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
