linux-kernel - Re: [Patch v4 01/13] x86/ioapic: Gate decrypted mapping on cc_platform

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Date:   Tue, 6 Dec 2022 20:22:52 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     hpa@...or.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, luto@...nel.org,
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        linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-arch@...r.kernel.org,
        iommu@...ts.linux.dev
Subject: Re: [Patch v4 01/13] x86/ioapic: Gate decrypted mapping on
 cc_platform_has() attribute

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?

Thx.

-- 
Regards/Gruss,
    Boris.

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