RE: [Patch v4 01/13] x86/ioapic: Gate decrypted mapping on cc_platform_has() attribute

[Michael Kelley (LINUX)]

From: Borislav Petkov <bp@xxxxxxxxx> Sent: Tuesday, December 6, 2022 11:23 AM
> 
> On Thu, Dec 01, 2022 at 07:30:19PM -0800, Michael Kelley wrote:
> > Current code always maps the IO-APIC as shared (decrypted) in a
> > confidential VM. But Hyper-V guest VMs on AMD SEV-SNP with vTOM
> > enabled use a paravisor running in VMPL0 to emulate the IO-APIC.
> > In such a case, the IO-APIC must be accessed as private (encrypted).
> 
> Lemme see I understand this correctly:
> 
> the paravisor is emulating the IO-APIC in the lower range of the address
> space, under the vTOM which is accessed encrypted.
> 
> That's why you need to access it encrypted in the guest.
> 
> Close?
> 

Exactly correct.

Michael