Re: [PATCH v3 0/8] Support ACPI PSP on Hyper-V

[Borislav Petkov]

On Wed, Mar 22, 2023 at 06:33:37PM +0100, Jeremi Piotrowski wrote:
> What this does is it allows a normal (non-SNP) VM to host confidential (SNP)
> VMs. I say "normal" but not every VM is going to be able to do this, it needs

If you say "non-SNP" VM then this sounds like purely for development.
Because I cannot see how you're going to give the confidentiality
guarantee to the SNP guests if the lower level is unencrypted, non-SNP
and so on...

> to be running on AMD hardware and configured to have access to
> VirtualizationExtensions, a "HardwareIsolation" capability, and given a number
> of "hardware isolated guests" that it is allowed to spawn. In practice this
> will result in the VM seeing a PSP device, SEV-SNP related CPUID
> leafs, and have access to additional memory management instructions
> (rmpadjust/psmash).  This allows the rest of the of KVM-SNP support to
> work.

So why don't you emulate the PSP in KVM instead of doing some BIOS hack?
And multiplex the access to it between all the parties needing it?

-- 
Regards/Gruss,
    Boris.

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