Re: [PATCH v3 0/8] Support ACPI PSP on Hyper-V

From: Borislav Petkov <bp@alien8.de>
To: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Cc: linux-kernel@vger.kernel.org,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"Kalra, Ashish" <ashish.kalra@amd.com>,
	linux-crypto@vger.kernel.org,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Len Brown <lenb@kernel.org>,
	linux-acpi@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org
Subject: Re: [PATCH v3 0/8] Support ACPI PSP on Hyper-V
Date: Thu, 23 Mar 2023 17:34:50 +0100	[thread overview]
Message-ID: <20230323163450.GGZBx/qpnclFnMaf7e@fat_crate.local> (raw)
In-Reply-To: <105d019c-2249-5dfd-e032-95944ea6dc8c@linux.microsoft.com>

On Thu, Mar 23, 2023 at 05:11:26PM +0100, Jeremi Piotrowski wrote:
> That same interface is exposed by physical hardware+firmware to the underlying
> Hyper-V.

Let me see if I understand it correctly: Hyper-V *baremetal* is using
the same ASPT spec to to talk to the *physical* PSP device?

Is that ASPT interface to talk to the PSP used by the L0 hypervisor?

Or does the L0 HV have a normal driver, similar to the Linux one,
without the functionality this ASPT spec provides?

> So it wasn't a matter of Microsoft architects coming up with a
> guest-host interface but rather exposing the virtual hardware in the same
> way as on a physical server.

So if you want to expose the same interface to the L1 guest, why isn't
Hyper-V emulating an ACPI device just like any other functionality? Why
does it need to reach into the interrupt handling internals?

I'd expect that the L0 HV would emulate a PSP device, the L1 would
simply load the Linux PSP device driver and everything should just work.

What's the point of that alternate access at all?

But I might still be missing something...

-- 
Regards/Gruss,
    Boris.

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