[PATCH v1 01/26] coco/tdx-host: Introduce a "tdx_host" device

[Xu Yilun <yilun.xu@linux.intel.com>]

From: Chao Gao <chao.gao@intel.com>

TDX depends on a platform firmware module that is invoked via instructions
similar to vmenter (i.e. enter into a new privileged "root-mode" context to
manage private memory and private device mechanisms). It is a software
construct that depends on the CPU vmxon state to enable invocation of
TDX-module ABIs. Unlike other Trusted Execution Environment (TEE) platform
implementations that employ a firmware module running on a PCI device with
an MMIO mailbox for communication, TDX has no hardware device to point to
as the TEE Secure Manager (TSM).

Create a virtual device not only to align with other implementations but
also to make it easier to

 - expose metadata (e.g., TDX module version, seamldr version etc) to
   the userspace as device attributes

 - implement firmware uploader APIs which are tied to a device. This is
   needed to support TDX module runtime updates

 - enable TDX Connect which will share a common infrastructure with other
   platform implementations. In the TDX Connect context, every
   architecture has a TSM, represented by a PCIe or virtual device. The
   new "tdx_host" device will serve the TSM role.

A faux device is used as for TDX because the TDX module is singular within
the system and lacks associated platform resources. Using a faux device
eliminates the need to create a stub bus.

The call to tdx_enable() makes the new module independent of kvm_intel.ko.
For example, TDX Connect may be used to established to PCIe link encryption
even if a TVM is never launched.  For now, just create the common loading
infrastructure.

[ Yilun: Remove unnecessary head files ]
Co-developed-by: Xu Yilun <yilun.xu@linux.intel.com>
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/virt/coco/Kconfig             |  2 ++
 drivers/virt/coco/tdx-host/Kconfig    | 10 +++++++
 drivers/virt/coco/Makefile            |  1 +
 drivers/virt/coco/tdx-host/Makefile   |  1 +
 drivers/virt/coco/tdx-host/tdx-host.c | 41 +++++++++++++++++++++++++++
 5 files changed, 55 insertions(+)
 create mode 100644 drivers/virt/coco/tdx-host/Kconfig
 create mode 100644 drivers/virt/coco/tdx-host/Makefile
 create mode 100644 drivers/virt/coco/tdx-host/tdx-host.c

diff --git a/drivers/virt/coco/Kconfig b/drivers/virt/coco/Kconfig
index bb0c6d6ddcc8..b9fb0760e917 100644
--- a/drivers/virt/coco/Kconfig
+++ b/drivers/virt/coco/Kconfig
@@ -15,5 +15,7 @@ source "drivers/virt/coco/arm-cca-guest/Kconfig"
 
 source "drivers/virt/coco/guest/Kconfig"
 
+source "drivers/virt/coco/tdx-host/Kconfig"
+
 config TSM
 	bool
diff --git a/drivers/virt/coco/tdx-host/Kconfig b/drivers/virt/coco/tdx-host/Kconfig
new file mode 100644
index 000000000000..bf6be0fc0879
--- /dev/null
+++ b/drivers/virt/coco/tdx-host/Kconfig
@@ -0,0 +1,10 @@
+config TDX_HOST_SERVICES
+	tristate "TDX Host Services Driver"
+	depends on INTEL_TDX_HOST
+	default m if INTEL_TDX_HOST
+	help
+	  Enable access to TDX host services like module update and
+	  extensions (e.g. TDX Connect).
+
+	  Say y or m if enabling support for confidential virtual machine
+	  support (CONFIG_INTEL_TDX_HOST). The module is called tdx_host.ko
diff --git a/drivers/virt/coco/Makefile b/drivers/virt/coco/Makefile
index cb52021912b3..b323b0ae4f82 100644
--- a/drivers/virt/coco/Makefile
+++ b/drivers/virt/coco/Makefile
@@ -6,6 +6,7 @@ obj-$(CONFIG_EFI_SECRET)	+= efi_secret/
 obj-$(CONFIG_ARM_PKVM_GUEST)	+= pkvm-guest/
 obj-$(CONFIG_SEV_GUEST)		+= sev-guest/
 obj-$(CONFIG_INTEL_TDX_GUEST)	+= tdx-guest/
+obj-$(CONFIG_INTEL_TDX_HOST)	+= tdx-host/
 obj-$(CONFIG_ARM_CCA_GUEST)	+= arm-cca-guest/
 obj-$(CONFIG_TSM) 		+= tsm-core.o
 obj-$(CONFIG_TSM_GUEST)		+= guest/
diff --git a/drivers/virt/coco/tdx-host/Makefile b/drivers/virt/coco/tdx-host/Makefile
new file mode 100644
index 000000000000..e61e749a8dff
--- /dev/null
+++ b/drivers/virt/coco/tdx-host/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_TDX_HOST_SERVICES) += tdx-host.o
diff --git a/drivers/virt/coco/tdx-host/tdx-host.c b/drivers/virt/coco/tdx-host/tdx-host.c
new file mode 100644
index 000000000000..ced1c980dc6f
--- /dev/null
+++ b/drivers/virt/coco/tdx-host/tdx-host.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * TDX host user interface driver
+ *
+ * Copyright (C) 2025 Intel Corporation
+ */
+
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/device/faux.h>
+#include <asm/cpu_device_id.h>
+
+static const struct x86_cpu_id tdx_host_ids[] = {
+	X86_MATCH_FEATURE(X86_FEATURE_TDX_HOST_PLATFORM, NULL),
+	{}
+};
+MODULE_DEVICE_TABLE(x86cpu, tdx_host_ids);
+
+static struct faux_device *fdev;
+
+static int __init tdx_host_init(void)
+{
+	if (!x86_match_cpu(tdx_host_ids))
+		return -ENODEV;
+
+	fdev = faux_device_create(KBUILD_MODNAME, NULL, NULL);
+	if (!fdev)
+		return -ENODEV;
+
+	return 0;
+}
+module_init(tdx_host_init);
+
+static void __exit tdx_host_exit(void)
+{
+	faux_device_destroy(fdev);
+}
+module_exit(tdx_host_exit);
+
+MODULE_DESCRIPTION("TDX Host Services");
+MODULE_LICENSE("GPL");
-- 
2.25.1