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

Jeremi Piotrowski
2023-02-01T14:10:03Z

On Tue, Jan 31, 2023 at 12:49:54PM -0600, Tom Lendacky wrote:
> 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

I'll do that. This will make the code depend on CONFIG_ARCH_HAS_CC_PLATFORM
and CONFIG_AMD_MEM_ENCRYPT, the latter selects the former. This will work
as long as CONFIG_AMD_MEM_ENCRYPT continues to be needed for both SNP guest
and host sides.

Jeremi

>
> > 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);