On Fri, Feb 10, 2023 at 11:47:27PM +0000, Sean Christopherson wrote:

I agree with Boris' comment that a one-off "other encrypted range" is a hack, but
that's just an API problem.  The kernel already has hypervisor specific hooks (and
for SEV-ES even), why not expand that?  That way figuring out which devices are
private is wholly contained in Hyper-V code, at least until there's a generic
solution for enumerating private devices, though that seems unlikely to happen
and will be a happy problem to solve if it does come about.

I feel ya and this all makes sense and your proposals look clean enough
to me but we still need some way of determining whether this is a vTOM
on hyperv because there's the next crapola with

https://lore.kernel.org/r/20230209072220.6836-4-jgross@suse.com (local)

because apparently hyperv does PAT but disables MTRRs for such vTOM
SEV-SNP guests and ... madness.

But that's not the only example - Xen has been doing this thing too.

And Jürgen has been trying to address this in a clean way but it is
a pain.

What I don't want to have is a gazillion ways to check what needs to
happen for which guest type. Because people who change the kernel to run
on baremetal, will break them. And I can't blame them. We try to support
all kinds of guests in the x86 code but this support should be plain and
simple.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette