On Fri, Feb 17, 2023, Borislav Petkov wrote:

On Fri, Feb 17, 2023 at 06:16:56AM +0000, Michael Kelley (LINUX) wrote:

quoted

Is that consistent with your thinking, or is the whole
cc_platform_has() approach problematic, including for the existing SEV
flavors and for TDX?

The confidential computing attributes are, yes, features. I've been
preaching since the very beginning that vTOM *is* *also* one such
feature. It is a feature bit in sev_features, for chrissakes. So by that
logic, those SEV-SNP HyperV guests should return true when

	cc_platform_has(CC_ATTR_GUEST_SEV_SNP_VTOM);

is tested.

But Sean doesn't like that.

Because vTOM is a hardware feature, whereas the IO-APIC and vTPM being accessible
via private memory are software features.  It's very possible to emulate the
IO-APIC in trusted code without vTOM.

If the access method to the IO-APIC and vTPM are specific to the
HyperV's vTOM implementation, then I don't mind if this were called

	cc_platform_has(CC_ATTR_GUEST_HYPERV_VTOM);

I still think that's likely to caused problems in the future, e.g. if Hyper-V
moves more stuff into the paravisor or if Hyper-V ends up with similar functionality
for TDX.  But it's not a sticking point, the only thing I'm fiercely resistant to
is conflating hardware features with software features.