On Fri, Feb 10, 2023, Sean Christopherson wrote:

On Fri, Feb 10, 2023, Dave Hansen wrote:

quoted

On 2/10/23 11:36, Borislav Petkov wrote:

quoted

quoted

One approach is to go with the individual device attributes for now.>> If the list does grow significantly, there will probably be patterns
or groupings that we can't discern now.  We could restructure into
larger buckets at that point based on those patterns/groupings.

There's a reason the word "platform" is in cc_platform_has(). Initially
we wanted to distinguish attributes of the different platforms. So even
if y'all don't like CC_ATTR_PARAVISOR, that is what distinguishes this
platform and it *is* one platform.

So call it CC_ATTR_SEV_VTOM as it uses that technology or whatever. But
call it like the platform, not to mean "I need this functionality".

I can live with that.  There's already a CC_ATTR_GUEST_SEV_SNP, so it
would at least not be too much of a break from what we already have.

I'm fine with CC_ATTR_SEV_VTOM, assuming the proposal is to have something like:

	static inline bool is_address_range_private(resource_size_t addr)
	{
		if (cc_platform_has(CC_ATTR_SEV_VTOM))
			return is_address_below_vtom(addr);

		return false;
	}

i.e. not have SEV_VTOM mean "I/O APIC and vTPM are private".  Though I don't see
the point in making it SEV vTOM specific or using a flag.  Despite what any of us
think about TDX paravisors, it's completely doable within the confines of TDX to
have an emulated device reside in the private address space.  E.g. why not
something like this? 

	static inline bool is_address_range_private(resource_size_t addr)
	{
		return addr < cc_platform_private_end;
	}

where SEV fills in "cc_platform_private_end" when vTOM is enabled, and TDX does
the same.  Or wrap cc_platform_private_end in a helper, etc.

Gah, forgot that the intent with TDX is to enumerate devices in their legacy
address spaces.  So a TDX guest couldn't do this by default, but if/when Hyper-V
or some other hypervisor moves I/O APIC, vTPM, etc... into the TCB, the common
code would just work and only the hypervisor-specific paravirt code would need
to change.

Probably need a more specific name than is_address_range_private() though, e.g.
is_mmio_address_range_private()?