cpus: don't use atomic_read for vm_clock_warp_start

As vm_clock_warp_start is a 64 bit value this causes problems for the
compiler trying to come up with a suitable atomic operation on 32 bit
hosts. Because the variable is protected by vm_clock_seqlock, we check its
value inside a seqlock critical section.

Signed-off-by: Alex Bennée <[email protected]>
Message-Id: <1459780549[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

diff --git a/cpus.c b/cpus.c
index 8ae477728d65758c4efc290b53107f960b1e630b..cbeb1f6139ea35de86b7684b5a527ae72bf306d4 100644 (file)
--- a/cpus.c
+++ b/cpus.c
@@ -338,10 +338,18 @@ static int64_t qemu_icount_round(int64_t count)
 
 static void icount_warp_rt(void)
 {
+    unsigned seq;
+    int64_t warp_start;
+
     /* The icount_warp_timer is rescheduled soon after vm_clock_warp_start
      * changes from -1 to another value, so the race here is okay.
      */
-    if (atomic_read(&vm_clock_warp_start) == -1) {
+    do {
+        seq = seqlock_read_begin(&timers_state.vm_clock_seqlock);
+        warp_start = vm_clock_warp_start;
+    } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, seq));
+
+    if (warp_start == -1) {
         return;
     }