[Qemu-devel] [PATCH] Fix qemu hang when i386 Linux host resumes from suspend

["Ed Swierk" <eswierk@arastra.com>]

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qemu hangs when an i386 Linux host resumes from suspend (swsusp2),
because the host's TSC is reset to a value lower than it was before
the suspend.

Although this is a bug in the host OS, the attached patch (originally
from John Coiner) is simple and makes qemu more resilient to weird
host tick counter behavior.

--Ed

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diff -BurN qemu-snapshot-2006-03-27_23.orig/vl.c qemu-snapshot-2006-03-27_23/vl.c
--- qemu-snapshot-2006-03-27_23.orig/vl.c	2006-04-01 18:38:27.000000000 +0000
+++ qemu-snapshot-2006-03-27_23/vl.c	2006-04-01 18:41:36.000000000 +0000
@@ -579,14 +579,21 @@
 #error unsupported CPU
 #endif
 
-static int64_t cpu_ticks_offset;
-static int cpu_ticks_enabled;
+static int64_t cpu_ticks_prev;
+static int64_t cpu_ticks_offset;
+static int cpu_ticks_enabled;
 
 static inline int64_t cpu_get_ticks(void)
 {
     if (!cpu_ticks_enabled) {
         return cpu_ticks_offset;
     } else {
+        int64_t ticks;
+        ticks = cpu_get_real_ticks();
+        if (cpu_ticks_prev > ticks) {
+            cpu_ticks_offset += cpu_ticks_prev - ticks;
+        }
+        cpu_ticks_prev = ticks;
-        return cpu_get_real_ticks() + cpu_ticks_offset;
+        return ticks + cpu_ticks_offset;
     }
 }