[Qemu-devel] [PATCH] replace while loop with a disabled wait on s390 bios

[Christian Borntraeger <borntraeger@de.ibm.com>]

dont waste cpu power on an error condition. Lets stop the guest
with a disabled wait.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 pc-bios/s390-ccw/main.c     |  4 ++--
 pc-bios/s390-ccw/s390-ccw.h |  3 +++
 pc-bios/s390-ccw/start.S    | 15 +++++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/pc-bios/s390-ccw/main.c b/pc-bios/s390-ccw/main.c
index 0913aac..c00f702 100644
--- a/pc-bios/s390-ccw/main.c
+++ b/pc-bios/s390-ccw/main.c
@@ -16,7 +16,7 @@ char stack[PAGE_SIZE * 8] __attribute__((__aligned__(PAGE_SIZE)));
 void virtio_panic(const char *string)
 {
     sclp_print(string);
-    while (1) { }
+    disabled_wait();
 }
 
 static void virtio_setup(void)
@@ -52,5 +52,5 @@ int main(void)
     virtio_setup();
     if (zipl_load() < 0)
         sclp_print("Failed to load OS from hard disk\n");
-    while (1) { }
+    disabled_wait();
 }
diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h
index a03dbaf..8241b0a 100644
--- a/pc-bios/s390-ccw/s390-ccw.h
+++ b/pc-bios/s390-ccw/s390-ccw.h
@@ -45,6 +45,9 @@ typedef unsigned long long __u64;
 
 #include "cio.h"
 
+/* start.s */
+void disabled_wait(void);
+
 /* main.c */
 void virtio_panic(const char *string);
 
diff --git a/pc-bios/s390-ccw/start.S b/pc-bios/s390-ccw/start.S
index c2b9a19..09deee7 100644
--- a/pc-bios/s390-ccw/start.S
+++ b/pc-bios/s390-ccw/start.S
@@ -3,6 +3,7 @@
  * into the pc-bios directory of qemu.
  *
  * Copyright (c) 2013 Alexander Graf <agraf@suse.de>
+ * Copyright 2013 IBM Corp.
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or (at
  * your option) any later version. See the COPYING file in the top-level
@@ -14,3 +15,17 @@ _start:
 
 larl	%r15, stack + 0x8000    /* Set up stack */
 j	main                    /* And call C */
+
+/*
+ * void disabled_wait(void)
+ *
+ * stops the current guest cpu.
+ */
+	.globl disabled_wait
+disabled_wait:
+        larl %r1,disabled_wait_psw
+        lpswe   0(%r1)
+
+        .align  8
+disabled_wait_psw:
+        .quad   0x0002000180000000,0x0000000000000000
-- 
1.8.1.4