linux-kernel - Re: [PATCH v3 3/8] x86/psp: Register PSP platform device when ASP table is present

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Message-ID: <6d3d512b-55e9-8205-461c-02f1e71f2b63@linux.microsoft.com>
Date:   Mon, 20 Mar 2023 20:37:56 +0100
From:   Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Subject: Re: [PATCH v3 3/8] x86/psp: Register PSP platform device when ASP
 table is present

On 20/03/2023 20:25, Borislav Petkov wrote:
> On Mon, Mar 20, 2023 at 07:19:51PM +0000, Jeremi Piotrowski wrote:
>> The ASP table contains the memory location of the register window for
>> communication with the Platform Security Processor. The device is not
>> exposed as an acpi node, so it is necessary to probe for the table and
>> register a platform_device to represent it in the kernel.
>>
>> At least conceptually, the same PSP may be exposed on the PCIe bus as
>> well, in which case it would be necessary to choose whether to use a PCI
>> BAR or the register window defined in ASPT for communication. There is
>> no advantage to using the ACPI and there are no known bare-metal systems
>> that expose the ASP table, so device registration is restricted to the
>> only systems known to provide an ASPT: Hyper-V VMs. Hyper-V VMs also do
>> not expose the PSP over PCIe.
>>
>> This is a skeleton device at this point, as the ccp driver is not yet
>> prepared to correctly probe it. Interrupt configuration will come later
>> on as well.
>>
>> Acked-by: Tom Lendacky <thomas.lendacky@....com>
>> Signed-off-by: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
>> ---
>>  arch/x86/kernel/Makefile |  1 +
>>  arch/x86/kernel/psp.c    | 42 ++++++++++++++++++++++++++++++++++++++++
> 
> If this is a platform device (driver), why isn't it part of
> the drivers/platform/x86/ lineup?
> 

Because of patch 4. My thinking was that the irq setup requires poking
at intimate architectural details (init_irq_alloc_info etc.) so it seems
like it fits in arch/x86.

I also drew inspiration from the sev-guest device in the arch/x86/kernel/sev.c,
which is used in a similar context (the PSP device I am registering here is
for SNP-host support).

Would you prefer it in drivers/platform/x86?

Jeremi