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

Tom Lendacky
2023-01-31T18:50:19Z

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@linux.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);