linux-kernel - [RFC PATCH 18/20] x86/virt/tdx: Update tdx_sysinfo and check features post-update

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Message-ID: <20250523095322.88774-19-chao.gao@intel.com>
Date: Fri, 23 May 2025 02:52:41 -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 18/20] x86/virt/tdx: Update tdx_sysinfo and check features post-update

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 TD-Preserving-capable 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@...el.com>
Tested-by: Farrah Chen <farrah.chen@...el.com>
---
 arch/x86/virt/vmx/tdx/seamldr.c | 13 ++++++++-
 arch/x86/virt/vmx/tdx/tdx.c     | 51 +++++++++++++++++++++++++++++++++
 arch/x86/virt/vmx/tdx/tdx.h     |  1 +
 3 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/arch/x86/virt/vmx/tdx/seamldr.c b/arch/x86/virt/vmx/tdx/seamldr.c
index 168fd2afd0c9..93385db56281 100644
--- a/arch/x86/virt/vmx/tdx/seamldr.c
+++ b/arch/x86/virt/vmx/tdx/seamldr.c
@@ -361,9 +361,16 @@ DEFINE_FREE(free_seamldr_params, struct seamldr_params *,
 
 static int seamldr_install_module(const u8 *data, u32 size)
 {
+	struct tdx_sys_info *info __free(kfree) = kzalloc(sizeof(*info),
+							  GFP_KERNEL);
+	int ret;
+
 	if (!td_preserving_ready)
 		return -EOPNOTSUPP;
 
+	if (!info)
+		return -ENOMEM;
+
 	struct seamldr_params *params __free(free_seamldr_params) =
 						init_seamldr_params(data, size);
 	if (IS_ERR(params))
@@ -371,7 +378,11 @@ static int seamldr_install_module(const u8 *data, u32 size)
 
 	atomic_set(&tdp_data.failed, 0);
 	set_state(TDP_START + 1);
-	return stop_machine(do_seamldr_install_module, params, cpu_online_mask);
+	ret = stop_machine(do_seamldr_install_module, params, cpu_online_mask);
+	if (ret)
+		return ret;
+
+	return tdx_module_post_update(info);
 }
 
 static enum fw_upload_err tdx_fw_prepare(struct fw_upload *fwl,
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 5f678c9da4ee..55bdc99818a1 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1406,6 +1406,57 @@ int tdx_module_run_update(void)
 	return ret;
 }
 
+/*
+ * Update tdx_sysinfo and check if any TDX module features changed after
+ * updates
+ */
+static void tdx_module_sysinfo_update_and_check(struct tdx_sys_info *info)
+{
+	struct tdx_sys_info_versions *old, *new;
+
+	guard(mutex)(&tdx_module_lock);
+
+	old = &tdx_sysinfo.versions;
+	new = &info->versions;
+	pr_info("version %d.%d.%d -> %d.%d.%d\n", old->major_version,
+						  old->minor_version,
+						  old->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.versions	= info->versions;
+	tdx_sysinfo.handoff	= info->handoff;
+
+	if (!memcmp(&tdx_sysinfo, info, sizeof(*info)))
+		return;
+
+	pr_info("TDX module features have changed after updates, but might not take effect.\n");
+	pr_info("Please consider a potential BIOS update.\n");
+}
+
+int tdx_module_post_update(struct tdx_sys_info *info)
+{
+	int ret;
+
+	/* Shouldn't fail as the update has succeeded */
+	ret = get_tdx_sys_info(info);
+	if (WARN_ON_ONCE(ret))
+		return ret;
+
+	tdx_module_sysinfo_update_and_check(info);
+	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 a05e3c21e7f5..57ccceba5406 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -128,5 +128,6 @@ int seamldr_prerr(u64 fn, struct tdx_module_args *args);
 int tdx_module_shutdown(void);
 void tdx_module_set_error(void);
 int tdx_module_run_update(void);
+int tdx_module_post_update(struct tdx_sys_info *info);
 
 #endif
-- 
2.47.1