linux-kernel - Re: [PATCH v1 3/8] x86/psp: Register PSP platform device when ASP table is present

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Date:   Tue, 31 Jan 2023 12:49:54 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>,
        linux-kernel@...r.kernel.org
Cc:     Brijesh Singh <brijesh.singh@....com>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Subject: Re: [PATCH v1 3/8] x86/psp: Register PSP platform device when ASP
 table is present

On 1/23/23 09:22, 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.
> 
> Signed-off-by: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
> ---
>   arch/x86/kernel/Makefile |  2 +-
>   arch/x86/kernel/psp.c    | 39 +++++++++++++++++++++++++++++++++++++++

Based on comments about other SEV related items, this should probably be 
moved into the arch/x86/coco/sev/ directory.

Thanks,
Tom

>   2 files changed, 40 insertions(+), 1 deletion(-)
>   create mode 100644 arch/x86/kernel/psp.c
> 
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index f901658d9f7c..e2e19f2d08a7 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -139,7 +139,7 @@ obj-$(CONFIG_UNWINDER_ORC)		+= unwind_orc.o
>   obj-$(CONFIG_UNWINDER_FRAME_POINTER)	+= unwind_frame.o
>   obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
>   
> -obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= sev.o
> +obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= psp.o sev.o
>   
>   obj-$(CONFIG_CFI_CLANG)			+= cfi.o
>   
> diff --git a/arch/x86/kernel/psp.c b/arch/x86/kernel/psp.c
> new file mode 100644
> index 000000000000..d404df47cc04
> --- /dev/null
> +++ b/arch/x86/kernel/psp.c
> @@ -0,0 +1,39 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/platform_data/psp.h>
> +#include <linux/platform_device.h>
> +#include <asm/hypervisor.h>
> +
> +static struct platform_device psp_device = {
> +	.name           = "psp",
> +	.id             = PLATFORM_DEVID_NONE,
> +};
> +
> +static int __init psp_init_platform_device(void)
> +{
> +	struct psp_platform_data pdata = {};
> +	struct resource res[1];
> +	int err;
> +
> +	/*
> +	 * The ACPI PSP interface is mutually exclusive with the PCIe interface,
> +	 * but there is no reason to use the ACPI interface over the PCIe one.
> +	 * Restrict probing ACPI PSP to platforms known to only expose the ACPI
> +	 * interface, which at this time is SNP-host capable Hyper-V VMs.
> +	 */
> +	if (!hypervisor_is_type(X86_HYPER_MS_HYPERV))
> +		return -ENODEV;
> +
> +	err = acpi_parse_aspt(res, &pdata);
> +	if (err)
> +		return err;
> +	err = platform_device_add_resources(&psp_device, res, 1);
> +	if (err)
> +		return err;
> +
> +	err = platform_device_register(&psp_device);
> +	if (err)
> +		return err;
> +	return 0;
> +}
> +device_initcall(psp_init_platform_device);