[efi] Work around temporal anomaly encountered during ExitBootServices()

EFI provides no clean way for device drivers to shut down in
preparation for handover to a booted operating system.  The platform
firmware simply doesn't bother to call the drivers' Stop() methods.
Instead, drivers must register an EVT_SIGNAL_EXIT_BOOT_SERVICES event
to be signalled when ExitBootServices() is called, and clean up
without any reference to the EFI driver model.

Unfortunately, all timers silently stop working when ExitBootServices()
is called.  Even more unfortunately, and for no discernible reason,
this happens before any EVT_SIGNAL_EXIT_BOOT_SERVICES events are
signalled.  The net effect of this entertaining design choice is that
any timeout loops on the shutdown path (e.g. for gracefully closing
outstanding TCP connections) may wait indefinitely.

There is no way to report failure from currticks(), since the API
lazily assumes that the host system continues to travel through time
in the usual direction.  Work around EFI's violation of this
assumption by falling back to a simple free-running monotonic counter.

Debugged-by: Maor Dickman <maord@mellanox.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

Author: mcb30

src/include/ipxe/efi/efi.h

@@ -214,6 +214,7 @@ extern EFI_HANDLE efi_image_handle;
 extern EFI_LOADED_IMAGE_PROTOCOL *efi_loaded_image;
 extern EFI_DEVICE_PATH_PROTOCOL *efi_loaded_image_path;
 extern EFI_SYSTEM_TABLE *efi_systab;
+extern int efi_shutdown_in_progress;
 
 extern const __attribute__ (( pure )) char * efi_guid_ntoa ( EFI_GUID *guid );
 extern const __attribute__ (( pure )) char *

src/interface/efi/efi_init.c

@@ -35,6 +35,9 @@ EFI_LOADED_IMAGE_PROTOCOL *efi_loaded_image;
 /** System table passed to entry point */
 EFI_SYSTEM_TABLE *efi_systab;
 
+/** EFI shutdown is in progress */
+int efi_shutdown_in_progress;
+
 /** Event used to signal shutdown */
 static EFI_EVENT efi_shutdown_event;
 
@@ -50,6 +53,13 @@ static EFI_STATUS EFIAPI efi_unload ( EFI_HANDLE image_handle );
  */
 static EFIAPI void efi_shutdown_hook ( EFI_EVENT event __unused,
 				       void *context __unused ) {
+
+	/* Mark shutdown as being in progress, to indicate that large
+	 * parts of the system (e.g. timers) are no longer functional.
+	 */
+	efi_shutdown_in_progress = 1;
+
+	/* Shut down iPXE */
 	shutdown_boot();
 }
 

src/interface/efi/efi_timer.c

@@ -70,6 +70,31 @@ static void efi_udelay ( unsigned long usecs ) {
  */
 static unsigned long efi_currticks ( void ) {
 
+	/* EFI provides no clean way for device drivers to shut down
+	 * in preparation for handover to a booted operating system.
+	 * The platform firmware simply doesn't bother to call the
+	 * drivers' Stop() methods.  Instead, drivers must register an
+	 * EVT_SIGNAL_EXIT_BOOT_SERVICES event to be signalled when
+	 * ExitBootServices() is called, and clean up without any
+	 * reference to the EFI driver model.
+	 *
+	 * Unfortunately, all timers silently stop working when
+	 * ExitBootServices() is called.  Even more unfortunately, and
+	 * for no discernible reason, this happens before any
+	 * EVT_SIGNAL_EXIT_BOOT_SERVICES events are signalled.  The
+	 * net effect of this entertaining design choice is that any
+	 * timeout loops on the shutdown path (e.g. for gracefully
+	 * closing outstanding TCP connections) may wait indefinitely.
+	 *
+	 * There is no way to report failure from currticks(), since
+	 * the API lazily assumes that the host system continues to
+	 * travel through time in the usual direction.  Work around
+	 * EFI's violation of this assumption by falling back to a
+	 * simple free-running monotonic counter.
+	 */
+	if ( efi_shutdown_in_progress )
+		efi_jiffies++;
+
 	return efi_jiffies;
 }