RE: [Patch v3 02/14] x86/ioapic: Gate decrypted mapping on cc_platform_has() attribute

Michael Kelley (LINUX)
2022-11-21T16:43:12Z

From: Borislav Petkov <bp@alien8.de> Sent: Monday, November 21, 2022 5:51 AM
>
> On Wed, Nov 16, 2022 at 10:41:25AM -0800, Michael Kelley wrote:
> > Current code always maps the IOAPIC 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 IOAPIC.
>
> "IO-APIC" I guess, in all your text.
>
> > In such a case, the IOAPIC must be accessed as private (encrypted).
>
> So the condition for the IO-APIC is pretty specific but the naming
> CC_ATTR_EMULATED_IOAPIC too generic. Other HVs emulate IO-APICs too,
> right?
>
> If you have to be precise, the proper check should be (pseudo code):
>
> if (cc_vendor(HYPERV) &&
> SNP enabled &&
> SNP features has vTOM &&
> paravisor in use)
>
> so I guess you're probably better off calling it
>
> CC_ATTR_ACCESS_IOAPIC_ENCRYPTED
>
> which then gets set on exactly those guests and nothing else.
>
> I'd say.
>

I'm OK with naming it very narrowly. When/if there's a more general
case later, we can generalize to whatever degree is appropriate.

Michael