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* [PATCH v10 10/25] coco/tdx-host: Expose P-SEAMLDR information via sysfs
@ 2026-05-20 13:38 Chao Gao
  2026-06-05 21:25 ` [tip: x86/tdx] " tip-bot2 for Chao Gao
  0 siblings, 1 reply; 2+ messages in thread
From: Chao Gao @ 2026-05-20 13:38 UTC (permalink / raw)
  To: kvm, linux-coco, linux-kernel
  Cc: binbin.wu, dave.hansen, djbw, ira.weiny, kai.huang, kas,
	nik.borisov, paulmck, pbonzini, reinette.chatre,
	rick.p.edgecombe, sagis, seanjc, tony.lindgren, vannapurve,
	vishal.l.verma, yilun.xu, xiaoyao.li, yan.y.zhao, Chao Gao,
	Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86,
	H. Peter Anvin

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. Make seamldr attributes
visible only when the update feature is supported, as that's their sole
purpose.

Note that the underlying P-SEAMLDR attributes are available regardless of
update support; this only restricts their visibility in Linux.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
---
v10:
 - Describe the P-SEAMLDR version by referring to the TDX module
   version instead of copying the text [Dave]
 - add a comment for DEVICE_ATTR_ADMIN_RO() [Dave]
 - Avoid the tertiary operator [Dave]
---
 .../ABI/testing/sysfs-devices-faux-tdx-host   | 21 ++++++
 arch/x86/include/asm/tdx.h                    |  6 ++
 drivers/virt/coco/tdx-host/tdx-host.c         | 72 ++++++++++++++++++-
 3 files changed, 98 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-faux-tdx-host b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
index 47d73cb89f1e..69b4cfc99d87 100644
--- a/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
+++ b/Documentation/ABI/testing/sysfs-devices-faux-tdx-host
@@ -3,3 +3,24 @@ Contact:	linux-coco@lists.linux.dev
 Description:	(RO) Report the version of the loaded TDX module.
 		Formatted as "major.minor.update". Used by TDX module
 		update tooling. Example: "1.2.03".
+
+What:		/sys/devices/faux/tdx_host/seamldr_version
+Contact:	linux-coco@lists.linux.dev
+Description:	(RO) Report the version of the loaded P-SEAMLDR.
+		Formatted as a TDX module version. Used by TDX module
+		update tooling.
+
+What:		/sys/devices/faux/tdx_host/num_remaining_updates
+Contact:	linux-coco@lists.linux.dev
+Description:	(RO) Report the number of remaining updates. TDX maintains a
+		log about each TDX module that has been loaded. This log has
+		a finite size, which limits the number of TDX 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 the P-SEAMLDR doesn't support updates.
+
+		See Intel® Trust Domain Extensions - SEAM Loader (SEAMLDR)
+		Interface Specification, Chapter "SEAMLDR_INFO" and Chapter
+		"SEAMLDR.INSTALL" for more information.
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index b7f4396b5cc5..27376db7ddac 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -110,6 +110,12 @@ void tdx_init(void);
 const char *tdx_dump_mce_info(struct mce *m);
 const struct tdx_sys_info *tdx_get_sysinfo(void);
 
+static inline bool tdx_supports_runtime_update(const struct tdx_sys_info *sysinfo)
+{
+	/* To be enabled when kernel is ready. */
+	return false;
+}
+
 int tdx_guest_keyid_alloc(void);
 u32 tdx_get_nr_guest_keyids(void);
 void tdx_guest_keyid_free(unsigned int keyid);
diff --git a/drivers/virt/coco/tdx-host/tdx-host.c b/drivers/virt/coco/tdx-host/tdx-host.c
index ef117a836b3a..2997311f72fa 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 <asm/cpu_device_id.h>
+#include <asm/seamldr.h>
 #include <asm/tdx.h>
 
 static const struct x86_cpu_id tdx_host_ids[] = {
@@ -40,7 +41,76 @@ static struct attribute *tdx_host_attrs[] = {
 	&dev_attr_version.attr,
 	NULL,
 };
-ATTRIBUTE_GROUPS(tdx_host);
+
+static const 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)
+{
+	struct seamldr_info info;
+	int ret;
+
+	ret = seamldr_get_info(&info);
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, TDX_VERSION_FMT "\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)
+{
+	struct seamldr_info info;
+	int ret;
+
+	ret = seamldr_get_info(&info);
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, "%u\n", info.num_remaining_updates);
+}
+
+/*
+ * These attributes are intended for managing TDX module updates. Reading
+ * them issues a slow, serialized P-SEAMLDR query, so keep them admin-only.
+ */
+static DEVICE_ATTR_ADMIN_RO(seamldr_version);
+static DEVICE_ATTR_ADMIN_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_visible(struct kobject *kobj, struct attribute *attr, int idx)
+{
+	const struct tdx_sys_info *sysinfo = tdx_get_sysinfo();
+
+	if (!sysinfo)
+		return 0;
+
+	if (!tdx_supports_runtime_update(sysinfo))
+		return 0;
+
+	return attr->mode;
+}
+
+static const struct attribute_group seamldr_group = {
+	.attrs = seamldr_attrs,
+	.is_visible = seamldr_group_visible,
+};
+
+static const struct attribute_group *tdx_host_groups[] = {
+	&tdx_host_group,
+	&seamldr_group,
+	NULL,
+};
 
 static struct faux_device *fdev;
 
-- 
2.52.0


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2026-05-22 17:26 ` [tip: x86/tdx] coco/tdx-host: Expose P-SEAMLDR information via sysfs tip-bot2 for Chao Gao
2026-05-20 13:38 [PATCH v10 10/25] " Chao Gao
2026-06-05 21:25 ` [tip: x86/tdx] " tip-bot2 for Chao Gao

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