[RFC PATCH v1 2/3] x86/tdx: Make TDX metadata available on guest via SYSFS

[Alexey Gladkov <legion@kernel.org>]

From: "Alexey Gladkov (Intel)" <legion@kernel.org>

Expose information about the TDX module to guest-side. TDX module
information (version, supported features, etc) is crucial for bug
reporting.

Signed-off-by: Alexey Gladkov (Intel) <legion@kernel.org>
---
 arch/x86/Kconfig        |  1 +
 arch/x86/coco/tdx/tdx.c | 92 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 516f3539d0c7..60f482edb1af 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -906,6 +906,7 @@ config INTEL_TDX_GUEST
 	select X86_MEM_ENCRYPT
 	select X86_MCE
 	select UNACCEPTED_MEMORY
+	select SYS_HYPERVISOR
 	help
 	  Support running as a guest under Intel TDX.  Without this support,
 	  the guest kernel can not boot or run under TDX.
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 32809a06dab4..86108735aaf1 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -8,6 +8,7 @@
 #include <linux/export.h>
 #include <linux/io.h>
 #include <linux/kexec.h>
+#include <linux/kobject.h>
 #include <asm/coco.h>
 #include <asm/tdx.h>
 #include <asm/vmx.h>
@@ -1051,6 +1052,97 @@ static __init void tdx_announce(void)
 	tdx_dump_td_ctls(controls);
 }
 
+#ifdef CONFIG_SYSFS
+static u64 tdx_read_sys_metadata_field(u64 field_id, u64 *data)
+{
+	struct tdx_module_args args = {};
+	u64 ret;
+
+	/*
+	 * TDH.SYS.RD -- reads one global metadata field
+	 *  - RDX (in): the field to read
+	 *  - R8 (out): the field data
+	 */
+	args.rdx = field_id;
+	ret = __tdcall_ret(TDG_SYS_RD, &args);
+
+	if (ret) {
+		pr_err("failed reading TDX field %llx, return %llx\n", field_id, ret);
+		return ret;
+	}
+
+	*data = args.r8;
+
+	return 0;
+}
+
+#define TDX_SYSFS_ATTR(_field, _name, fmt)				\
+static ssize_t _name ## _show(						\
+	struct kobject *kobj, struct kobj_attribute *attr, char *buf)	\
+{									\
+	u64 value = 0;							\
+	tdx_read_sys_metadata_field(_field, &value);			\
+	return sprintf(buf, fmt, value);				\
+}									\
+static struct kobj_attribute _name ## _attr = __ATTR_RO(_name)
+
+TDX_SYSFS_ATTR(TDX_SYS_MINOR_FID, minor, "%lld\n");
+TDX_SYSFS_ATTR(TDX_SYS_MAJOR_FID, major, "%lld\n");
+TDX_SYSFS_ATTR(TDX_SYS_FEATURES0_FID, features0, "%llx\n");
+
+static struct attribute *version_attrs[] = {
+	&minor_attr.attr,
+	&major_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group version_attr_group = {
+	.name = "version",
+	.attrs = version_attrs,
+};
+
+static struct attribute *properties_attrs[] = {
+	&features0_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group properties_attr_group = {
+	.name = "properties",
+	.attrs = properties_attrs,
+};
+
+static int tdx_sysfs_init(void)
+{
+	struct kobject *tdx_kobj;
+	int ret;
+
+	if (!hypervisor_kobj)
+		return -ENOMEM;
+
+	tdx_kobj = kobject_create_and_add("tdx", hypervisor_kobj);
+
+	if (!tdx_kobj)
+		return -ENOMEM;
+
+	ret = sysfs_create_group(tdx_kobj, &version_attr_group);
+	if (ret)
+		pr_err("sysfs exporting tdx module version failed %d\n", ret);
+
+	if (!ret) {
+		ret = sysfs_create_group(tdx_kobj, &properties_attr_group);
+		if (ret)
+			pr_err("sysfs exporting tdx module properties failed %d\n", ret);
+	}
+
+	if (ret)
+		kobject_put(tdx_kobj);
+
+	return ret;
+}
+
+arch_initcall(tdx_sysfs_init);
+#endif // CONFIG_SYSFS
+
 void __init tdx_early_init(void)
 {
 	u64 cc_mask;
-- 
2.48.1