[PATCH v7 02/22] coco/tdx-host: Introduce a "tdx_host" device

Chao Gao
2026-03-31T12:43:26Z

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 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_get_sysinfo() ensures that the TDX module is ready to
provide services.

Note that AMD has a PCI device for the PSP for SEV and ARM CCA will
likely have a faux device [1].

Co-developed-by: Xu Yilun <yilun.xu@linux.intel.com>
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Reviewed-by: Xu Yilun <yilun.xu@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/all/2025073035-bulginess-rematch-b92e@gregkh/ # [1]
---
v3:
- add Jonathan's reviewed-by
- add tdx_get_sysinfo() in module_init() to ensure the TDX module is up
and running.
- note in the changelog that both AMD and ARM have devices for coco
---
arch/x86/virt/vmx/tdx/tdx.c | 2 +-
drivers/virt/coco/Kconfig | 2 ++
drivers/virt/coco/Makefile | 1 +
drivers/virt/coco/tdx-host/Kconfig | 10 +++++++
drivers/virt/coco/tdx-host/Makefile | 1 +
drivers/virt/coco/tdx-host/tdx-host.c | 43 +++++++++++++++++++++++++++
6 files changed, 58 insertions(+), 1 deletion(-)
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/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 06d9709ade85..172f6d4133b5 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1435,7 +1435,7 @@ const struct tdx_sys_info *tdx_get_sysinfo(void)

return p;
}
-EXPORT_SYMBOL_FOR_KVM(tdx_get_sysinfo);
+EXPORT_SYMBOL_FOR_MODULES(tdx_get_sysinfo, "kvm-intel,tdx-host");

u32 tdx_get_nr_guest_keyids(void)
{
diff --git a/drivers/virt/coco/Kconfig b/drivers/virt/coco/Kconfig
index df1cfaf26c65..f7691f64fbe3 100644
--- a/drivers/virt/coco/Kconfig
+++ b/drivers/virt/coco/Kconfig
@@ -17,5 +17,7 @@ source "drivers/virt/coco/arm-cca-guest/Kconfig"
source "drivers/virt/coco/guest/Kconfig"
endif

+source "drivers/virt/coco/tdx-host/Kconfig"
+
config TSM
bool
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/Kconfig b/drivers/virt/coco/tdx-host/Kconfig
new file mode 100644
index 000000000000..d35d85ef91c0
--- /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
+ 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/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..c77885392b09
--- /dev/null
+++ b/drivers/virt/coco/tdx-host/tdx-host.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * TDX host user interface driver
+ *
+ * Copyright (C) 2025 Intel Corporation
+ */
+
+#include <linux/device/faux.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+
+#include <asm/cpu_device_id.h>
+#include <asm/tdx.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) || !tdx_get_sysinfo())
+ 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");
--
2.47.3