[PATCH v2 16/21] x86/virt/seamldr: Handle TDX Module update failures

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

Failures encountered after a successful module shutdown are unrecoverable,
e.g., there is no way to restore the old TDX Module.

All subsequent SEAMCALLs to the TDX Module will fail and so TDs have to be
killed.

Report failures through sysfs attributes and log a message to clarify that
SEAMCALL errors are expected in this situation.

To prevent TDX Module update failures, admins are encouraged to use the
user space tool [1] that will perform compatibility and integrity checks
that guarantee TDX Module update success (unless the system's update limit
is exceeded, but the kernel will prevent an update attempt in this case).

Signed-off-by: Chao Gao <chao.gao@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Link: https://github.com/intel/tdx-module-binaries/blob/main/version_select_and_load.py # [1]
---
 arch/x86/virt/vmx/tdx/seamldr.c       | 15 ++++++++++++++-
 arch/x86/virt/vmx/tdx/tdx.c           |  6 ++++++
 arch/x86/virt/vmx/tdx/tdx.h           |  1 +
 drivers/virt/coco/tdx-host/tdx-host.c |  4 ++++
 4 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/x86/virt/vmx/tdx/seamldr.c b/arch/x86/virt/vmx/tdx/seamldr.c
index b9daf11e1064..a5aff04a85b9 100644
--- a/arch/x86/virt/vmx/tdx/seamldr.c
+++ b/arch/x86/virt/vmx/tdx/seamldr.c
@@ -264,6 +264,14 @@ static void ack_state(void)
 	}
 }
 
+static void print_update_failure_message(void)
+{
+	static atomic_t printed = ATOMIC_INIT(0);
+
+	if (atomic_inc_return(&printed) == 1)
+		pr_err("update failed, SEAMCALLs will report failure until TDs killed\n");
+}
+
 /*
  * See multi_cpu_stop() from where this multi-cpu state-machine was
  * adopted, and the rationale for touch_nmi_watchdog()
@@ -293,8 +301,13 @@ static int do_seamldr_install_module(void *params)
 				break;
 			}
 
-			if (ret)
+			if (ret) {
 				atomic_inc(&tdp_data.failed);
+				if (curstate > TDP_SHUTDOWN) {
+					tdx_module_set_error();
+					print_update_failure_message();
+				}
+			}
 			ack_state();
 		} else {
 			touch_nmi_watchdog();
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 7019a149ec4b..26357be18fa9 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1219,6 +1219,12 @@ int tdx_module_shutdown(void)
 	return 0;
 }
 
+void tdx_module_set_error(void)
+{
+	/* Called from stop_machine(). no need to hold tdx_module_lock */
+	tdx_module_status = TDX_MODULE_ERROR;
+}
+
 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 1c4da9540ae0..5b9a2d63808c 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -120,5 +120,6 @@ struct tdmr_info_list {
 };
 
 int tdx_module_shutdown(void);
+void tdx_module_set_error(void);
 
 #endif
diff --git a/drivers/virt/coco/tdx-host/tdx-host.c b/drivers/virt/coco/tdx-host/tdx-host.c
index 418e90797689..47c5ba115993 100644
--- a/drivers/virt/coco/tdx-host/tdx-host.c
+++ b/drivers/virt/coco/tdx-host/tdx-host.c
@@ -37,6 +37,10 @@ static ssize_t version_show(struct device *dev, struct device_attribute *attr,
 	const struct tdx_sys_info *tdx_sysinfo = tdx_get_sysinfo();
 	const struct tdx_sys_info_version *ver;
 
+	/*
+	 * Inform userspace that the TDX module isn't in a usable state,
+	 * possibly due to a failed update.
+	 */
 	if (!tdx_sysinfo)
 		return -ENXIO;
 
-- 
2.47.3