On Mon, Nov 28, 2022 at 05:55:11PM +0000, Michael Kelley (LINUX) wrote:

But vendor AMD effectively offers two different encryption schemes that
could be seen by the guest VM.  The hypervisor chooses which scheme a
particular guest will see.  Hyper-V has chosen to present the vTOM scheme
to guest VMs, including normal Linux and Windows guests, that have been
modestly updated to understand vTOM.

If this is a standard SNP guest then you can detect vTOM support using
SEV_FEATURES. See this thread here:

https://lore.kernel.org/r/20221117044433.244656-1-nikunj@amd.com (local)

Which then means, you don't need any special gunk except extending this
patch above to check SNP has vTOM support.

In the future, Hyper-V may also choose to present original AMD C-bit scheme
in some guest VMs, depending on the use case.  And it will present the Intel
TDX scheme when running on that hardware.

And all those should JustWork(tm) because we already support such guests.

To my knowledge, KVM does not support the AMD vTOM scheme.
Someone from AMD may have a better sense whether adding that
support is likely in the future.

Yah, see above.

Thx.

-- 
Regards/Gruss,
    Boris.

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