x86, efi: retry ExitBootServices() on failure (bnc#823386).

suse-commit: 3935df2b3c2115b897a0f79a71c20035f052a821
diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index e152fb2..0a977e8 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -890,18 +890,20 @@
 	efi_memory_desc_t *mem_map;
 	efi_status_t status;
 	__u32 desc_version;
+	bool called_exit = false;
 	u8 nr_entries;
 	int i;
 
 	size = sizeof(*mem_map) * 32;
 
 again:
-	size += sizeof(*mem_map);
+	size += sizeof(*mem_map) * 2;
 	_size = size;
 	status = low_alloc(size, 1, (unsigned long *)&mem_map);
 	if (status != EFI_SUCCESS)
 		return status;
 
+get_map:
 	status = efi_call_phys5(sys_table->boottime->get_memory_map, &size,
 				mem_map, &key, &desc_size, &desc_version);
 	if (status == EFI_BUFFER_TOO_SMALL) {
@@ -927,8 +929,20 @@
 	/* Might as well exit boot services now */
 	status = efi_call_phys2(sys_table->boottime->exit_boot_services,
 				handle, key);
-	if (status != EFI_SUCCESS)
-		goto free_mem_map;
+	if (status != EFI_SUCCESS) {
+		/*
+		 * ExitBootServices() will fail if any of the event
+		 * handlers change the memory map. In which case, we
+		 * must be prepared to retry, but only once so that
+		 * we're guaranteed to exit on repeated failures instead
+		 * of spinning forever.
+		 */
+		if (called_exit)
+			goto free_mem_map;
+
+		called_exit = true;
+		goto get_map;
+	}
 
 	/* Historic? */
 	boot_params->alt_mem_k = 32 * 1024;