linux-kernel - [RFC PATCH 04/20] x86/virt/tdx: Introduce a "tdx" subsystem and "tsm" device

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Message-ID: <20250523095322.88774-5-chao.gao@intel.com>
Date: Fri, 23 May 2025 02:52:27 -0700
From: Chao Gao <chao.gao@...el.com>
To: linux-coco@...ts.linux.dev,
	x86@...nel.org,
	kvm@...r.kernel.org
Cc: seanjc@...gle.com,
	pbonzini@...hat.com,
	eddie.dong@...el.com,
	kirill.shutemov@...el.com,
	dave.hansen@...el.com,
	dan.j.williams@...el.com,
	kai.huang@...el.com,
	isaku.yamahata@...el.com,
	elena.reshetova@...el.com,
	rick.p.edgecombe@...el.com,
	Chao Gao <chao.gao@...el.com>,
	Farrah Chen <farrah.chen@...el.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH 04/20] x86/virt/tdx: Introduce a "tdx" subsystem and "tsm" device

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 "TSM".

The "/sys/devices/virtual" hierarchy is intended for "software
constructs which need sysfs interface", which aligns with what TDX
needs.

The new tdx_subsys will export global attributes populated by the
TDX-module "sysinfo". A tdx_tsm device is published on this bus to
enable a typical driver model for the low level "TEE Security Manager"
(TSM) flows that talk TDISP to capable PCIe devices.

For now, this is only the base tdx_subsys and tdx_tsm device
registration with attribute definition and TSM driver to follow later.

Co-developed-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Chao Gao <chao.gao@...el.com>
Tested-by: Farrah Chen <farrah.chen@...el.com>
---
 arch/x86/virt/vmx/tdx/tdx.c | 75 +++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index b586329dd87d..9719df2f2634 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -28,6 +28,8 @@
 #include <linux/log2.h>
 #include <linux/acpi.h>
 #include <linux/suspend.h>
+#include <linux/device.h>
+#include <linux/cleanup.h>
 #include <linux/idr.h>
 #include <asm/page.h>
 #include <asm/special_insns.h>
@@ -1080,6 +1082,77 @@ static int init_tdmrs(struct tdmr_info_list *tdmr_list)
 	return 0;
 }
 
+static const struct bus_type tdx_subsys = {
+	.name = "tdx",
+};
+
+struct tdx_tsm {
+	struct device dev;
+};
+
+static struct tdx_tsm *alloc_tdx_tsm(void)
+{
+	struct tdx_tsm *tsm = kzalloc(sizeof(*tsm), GFP_KERNEL);
+	struct device *dev;
+
+	if (!tsm)
+		return ERR_PTR(-ENOMEM);
+
+	dev = &tsm->dev;
+	dev->bus = &tdx_subsys;
+	device_initialize(dev);
+
+	return tsm;
+}
+
+DEFINE_FREE(tdx_tsm_put, struct tdx_tsm *,
+	    if (!IS_ERR_OR_NULL(_T)) put_device(&_T->dev))
+static struct tdx_tsm *init_tdx_tsm(void)
+{
+	struct device *dev;
+	int ret;
+
+	struct tdx_tsm *tsm __free(tdx_tsm_put) = alloc_tdx_tsm();
+	if (IS_ERR(tsm))
+		return tsm;
+
+	dev = &tsm->dev;
+	ret = dev_set_name(dev, "tdx_tsm");
+	if (ret)
+		return ERR_PTR(ret);
+
+	ret = device_add(dev);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return no_free_ptr(tsm);
+}
+
+static void tdx_subsys_init(void)
+{
+	struct tdx_tsm *tdx_tsm;
+	int err;
+
+	/* Establish subsystem for global TDX module attributes */
+	err = subsys_virtual_register(&tdx_subsys, NULL);
+	if (err) {
+		pr_err("failed to register tdx_subsys %d\n", err);
+		return;
+	}
+
+	/* Register 'tdx_tsm' for driving optional TDX Connect functionality */
+	tdx_tsm = init_tdx_tsm();
+	if (IS_ERR(tdx_tsm)) {
+		pr_err("failed to initialize TSM device (%pe)\n", tdx_tsm);
+		goto err_bus;
+	}
+
+	return;
+
+err_bus:
+	bus_unregister(&tdx_subsys);
+}
+
 static int init_tdx_module(void)
 {
 	int ret;
@@ -1136,6 +1209,8 @@ static int init_tdx_module(void)
 
 	pr_info("%lu KB allocated for PAMT\n", tdmrs_count_pamt_kb(&tdx_tdmr_list));
 
+	tdx_subsys_init();
+
 out_put_tdxmem:
 	/*
 	 * @tdx_memlist is written here and read at memory hotplug time.
-- 
2.47.1