linux-kernel - Re: [Patch v3 02/14] x86/ioapic: Gate decrypted mapping on cc_platform

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Date:   Mon, 21 Nov 2022 14:50:36 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     hpa@...or.com, kys@...rosoft.com, haiyangz@...rosoft.com,
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Subject: Re: [Patch v3 02/14] x86/ioapic: Gate decrypted mapping on
 cc_platform_has() attribute

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.

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