firmware_uefi: EfiDiagnostics should flush when unprocessed after reset or shutdown

vm/devices/firmware/firmware_uefi/src/lib.rs

@@ -341,14 +341,39 @@ impl UefiDevice {
             Result::<_, std::convert::Infallible>::Ok(output.unwrap_or_else(|| USAGE.to_string()))
         });
     }
+
+    /// Process diagnostics if a GPA has been configured but logs have not yet
+    /// been processed.
+    fn process_pending_diagnostics(&mut self, trigger: &'static str) {
+        if self.service.diagnostics.has_unprocessed_diagnostics() {
+            tracing::info!(%trigger, "processing pending UEFI diagnostics");
+            let _ = self.process_diagnostics(
+                false,
+                service::diagnostics::DiagnosticsEmitter::Tracing { limit: None },
+                Some(LogLevel::make_info()),
+            );
+        }
+    }
+}
+
+impl Drop for UefiDevice {
+    fn drop(&mut self) {
+        // Best-effort fallback for teardown paths that do not invoke explicit
+        // ChangeDeviceState::stop/reset transitions.
+        self.process_pending_diagnostics("drop");
+    }
 }
 
 impl ChangeDeviceState for UefiDevice {
     fn start(&mut self) {}
 
-    async fn stop(&mut self) {}
+    async fn stop(&mut self) {
+        self.process_pending_diagnostics("stop");
+    }
 
     async fn reset(&mut self) {
+        self.process_pending_diagnostics("reset");
+
         self.address = 0;
 
         self.service.nvram.reset();

vm/devices/firmware/firmware_uefi/src/service/diagnostics/mod.rs

@@ -178,6 +178,15 @@ impl DiagnosticsServices {
         self.processed = false;
     }
 
+    /// Returns true if a GPA has been set and diagnostics have not yet been processed.
+    ///
+    /// Used to detect cases where the guest resets or shuts down without going through
+    /// the normal UEFI crash path or ExitBootServices, so that the caller can trigger
+    /// processing before discarding the buffer.
+    pub fn has_unprocessed_diagnostics(&self) -> bool {
+        self.gpa.is_some() && !self.processed
+    }
+
     /// Set the GPA of the diagnostics buffer
     pub fn set_gpa(&mut self, gpa: u32) {
         self.gpa = Gpa::new(gpa).ok();