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

Borislav Petkov
2022-11-21T13:50:47Z

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.

Thx.

--
Regards/Gruss,
Boris.