[PATCH v2 20/21] x86/virt/tdx: Update tdx_sysinfo and check features post-update

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

tdx_sysinfo contains all metadata of the active TDX module, including
versions, supported features, and TDMR/TDCS/TDVPS information. These
elements may change over updates. Blindly refreshing the entire tdx_sysinfo
could disrupt running software, as it may subtly rely on the previous state
unless proven otherwise.

Adopt a conservative approach, like microcode updates, by only refreshing
version information that does not affect functionality, while ignoring
all other changes. This is acceptable as new modules are required to
maintain backward compatibility.

Any updates to metadata beyond versions should be justified and reviewed on
a case-by-case basis.

Note that preallocating a tdx_sys_info buffer before updates is to avoid
having to handle -ENOMEM when updating tdx_sysinfo after a successful
update.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
---
v2:
 - don't add a separate function for version and feature checks. Do them
   directly in tdx_module_post_update()
 - add a comment about preallocating a tdx_sys_info buffer in
   seamldr_install_module().
---
 arch/x86/virt/vmx/tdx/seamldr.c | 12 ++++++++-
 arch/x86/virt/vmx/tdx/tdx.c     | 47 +++++++++++++++++++++++++++++++++
 arch/x86/virt/vmx/tdx/tdx.h     |  2 ++
 3 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/arch/x86/virt/vmx/tdx/seamldr.c b/arch/x86/virt/vmx/tdx/seamldr.c
index a8ca6966beac..a72f6b0b27e9 100644
--- a/arch/x86/virt/vmx/tdx/seamldr.c
+++ b/arch/x86/virt/vmx/tdx/seamldr.c
@@ -350,6 +350,16 @@ int seamldr_install_module(const u8 *data, u32 size)
 	if (!info->num_remaining_updates)
 		return -ENOSPC;
 
+	/*
+	 * Preallocating a tdx_sys_info buffer before updates is to avoid having to
+	 * handle -ENOMEM when updating tdx_sysinfo after a successful update.
+	 */
+	struct tdx_sys_info *sysinfo __free(kfree) = kzalloc(sizeof(*sysinfo),
+							     GFP_KERNEL);
+	if (!sysinfo)
+		return -ENOMEM;
+
+
 	struct seamldr_params *params __free(free_seamldr_params) =
 						init_seamldr_params(data, size);
 	if (IS_ERR(params))
@@ -367,6 +377,6 @@ int seamldr_install_module(const u8 *data, u32 size)
 	if (ret)
 		return ret;
 
-	return 0;
+	return tdx_module_post_update(sysinfo);
 }
 EXPORT_SYMBOL_GPL_FOR_MODULES(seamldr_install_module, "tdx-host");
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 7613fd16a0ce..128e6ffba736 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1241,6 +1241,53 @@ int tdx_module_run_update(void)
 	return 0;
 }
 
+/*
+ * Update tdx_sysinfo and check if any TDX module features changed after
+ * updates
+ */
+int tdx_module_post_update(struct tdx_sys_info *info)
+{
+	struct tdx_sys_info_version *cur, *new;
+	int ret;
+
+	/* Shouldn't fail as the update has succeeded */
+	ret = get_tdx_sys_info(info);
+	if (ret) {
+		WARN_ONCE(1, "version retrieval failed after update, replace TDX Module\n");
+		return ret;
+	}
+
+	guard(mutex)(&tdx_module_lock);
+
+	cur = &tdx_sysinfo.version;
+	new = &info->version;
+	pr_info("version %u.%u.%02u -> %u.%u.%02u\n", cur->major_version,
+						      cur->minor_version,
+						      cur->update_version,
+						      new->major_version,
+						      new->minor_version,
+						      new->update_version);
+
+	/*
+	 * Blindly refreshing the entire tdx_sysinfo could disrupt running
+	 * software, as it may subtly rely on the previous state unless
+	 * proven otherwise.
+	 *
+	 * Only refresh version information (including handoff version)
+	 * that does not affect functionality, and ignore all other
+	 * changes.
+	 */
+	tdx_sysinfo.version	= info->version;
+	tdx_sysinfo.handoff	= info->handoff;
+
+	if (!memcmp(&tdx_sysinfo, info, sizeof(*info)))
+		return 0;
+
+	pr_info("TDX module features have changed after updates, but might not take effect.\n");
+	pr_info("Please consider a potential BIOS update.\n");
+	return 0;
+}
+
 static bool is_pamt_page(unsigned long phys)
 {
 	struct tdmr_info_list *tdmr_list = &tdx_tdmr_list;
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
index 983c01c6949a..ca76126880ee 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -3,6 +3,7 @@
 #define _X86_VIRT_TDX_H
 
 #include <linux/bits.h>
+#include <asm/tdx_global_metadata.h>
 
 /*
  * This file contains both macros and data structures defined by the TDX
@@ -124,5 +125,6 @@ int tdx_module_shutdown(void);
 void tdx_module_set_error(void);
 int tdx_cpu_enable(void);
 int tdx_module_run_update(void);
+int tdx_module_post_update(struct tdx_sys_info *info);
 
 #endif
-- 
2.47.3