[PATCH v2 07/21] coco/tdx-host: Expose P-SEAMLDR information via sysfs

[Chao Gao <chao.gao@intel.com>]

TDX Module updates require userspace to select the appropriate module
to load. Expose necessary information to facilitate this decision. Two
values are needed:

- P-SEAMLDR version: for compatibility checks between TDX Module and
		     P-SEAMLDR
- num_remaining_updates: indicates how many updates can be performed

Expose them as tdx-host device attributes.

Note that P-SEAMLDR sysfs nodes are hidden when INTEL_TDX_MODULE_UPDATE
isn't enabled or when P-SEAMLDR isn't loaded by BIOS, both of which
cause seamldr_get_info() to return NULL.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
---
 .../ABI/testing/sysfs-devices-faux-tdx-host   | 25 ++++++++
 drivers/virt/coco/tdx-host/tdx-host.c         | 63 ++++++++++++++++++-
 2 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-faux-tdx-host b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
index 18d4a4a71b80..13c1f4f9909c 100644
--- a/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
+++ b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
@@ -4,3 +4,28 @@ Description:	(RO) Report the version of the loaded TDX module. The TDX module
 		version is formatted as x.y.z, where "x" is the major version,
 		"y" is the minor version and "z" is the update version. Versions
 		are used for bug reporting, TD-Preserving updates and etc.
+
+What:		/sys/devices/faux/tdx_host/seamldr/version
+Contact:	linux-coco@lists.linux.dev
+Description:	(RO) Report the version of the loaded SEAM loader. The SEAM
+		loader version is formatted as x.y.z, where "x" is the major
+		version, "y" is the minor version and "z" is the update version.
+		Versions are used for bug reporting and compatibility check.
+
+What:		/sys/devices/faux/tdx_host/seamldr/num_remaining_updates
+Contact:	linux-coco@lists.linux.dev
+Description:	(RO) Report the number of remaining updates that can be performed.
+		The CPU keeps track of TCB versions for each TDX Module that
+		has been loaded. Since this tracking database has finite
+		capacity, there's a maximum number of module updates that can
+		be performed.
+
+		After each successful update, the number reduces by one. Once it
+		reaches zero, further updates will fail until next reboot. The
+		number is always zero if P-SEAMLDR doesn't support updates.
+
+		See Intel® Trust Domain Extensions - SEAM Loader (SEAMLDR)
+		Interface Specification Chapter 3.3 "SEAMLDR_INFO" and Chapter
+		4.2 "SEAMLDR.INSTALL" for more information. The documentation is
+		available at:
+		https://cdrdv2-public.intel.com/739045/intel-tdx-seamldr-interface-specification.pdf
diff --git a/drivers/virt/coco/tdx-host/tdx-host.c b/drivers/virt/coco/tdx-host/tdx-host.c
index 968a19f4e01a..42570c5b221b 100644
--- a/drivers/virt/coco/tdx-host/tdx-host.c
+++ b/drivers/virt/coco/tdx-host/tdx-host.c
@@ -11,6 +11,7 @@
 #include <linux/sysfs.h>
 #include <linux/device/faux.h>
 #include <asm/cpu_device_id.h>
+#include <asm/seamldr.h>
 #include <asm/tdx.h>
 #include <asm/tdx_global_metadata.h>
 
@@ -43,7 +44,67 @@ static struct attribute *tdx_host_attrs[] = {
 	&dev_attr_version.attr,
 	NULL,
 };
-ATTRIBUTE_GROUPS(tdx_host);
+
+struct attribute_group tdx_host_group = {
+	.attrs = tdx_host_attrs,
+};
+
+static ssize_t seamldr_version_show(struct device *dev, struct device_attribute *attr,
+				    char *buf)
+{
+	const struct seamldr_info *info = seamldr_get_info();
+
+	if (!info)
+		return -ENXIO;
+
+	return sysfs_emit(buf, "%u.%u.%u\n", info->major_version,
+					     info->minor_version,
+					     info->update_version);
+}
+
+static ssize_t num_remaining_updates_show(struct device *dev,
+					  struct device_attribute *attr,
+					  char *buf)
+{
+	const struct seamldr_info *info = seamldr_get_info();
+
+	if (!info)
+		return -ENXIO;
+
+	return sysfs_emit(buf, "%u\n", info->num_remaining_updates);
+}
+
+/*
+ * Open-code DEVICE_ATTR_RO to specify a different 'show' function for
+ * P-SEAMLDR version as version_show() is used for the TDX Module version.
+ */
+static struct device_attribute dev_attr_seamldr_version =
+	__ATTR(version, 0444, seamldr_version_show, NULL);
+static DEVICE_ATTR_RO(num_remaining_updates);
+
+static struct attribute *seamldr_attrs[] = {
+	&dev_attr_seamldr_version.attr,
+	&dev_attr_num_remaining_updates.attr,
+	NULL,
+};
+
+static umode_t seamldr_group_is_visible(struct kobject *kobj,
+					struct attribute *attr, int n)
+{
+	return seamldr_get_info() ? attr->mode : 0;
+}
+
+static struct attribute_group seamldr_group = {
+	.name = "seamldr",
+	.attrs = seamldr_attrs,
+	.is_visible = seamldr_group_is_visible,
+};
+
+static const struct attribute_group *tdx_host_groups[] = {
+	&tdx_host_group,
+	&seamldr_group,
+	NULL,
+};
 
 static int __init tdx_host_init(void)
 {
-- 
2.47.3