From ccffff48c93c30733783b05cd1ef843a4c274653 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20Benn=C3=A9e?= <alex.bennee@linaro.org>
Date: Mon, 4 Apr 2016 15:35:48 +0100
Subject: [PATCH] cpus: don't use atomic_read for vm_clock_warp_start
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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 <alex.bennee@linaro.org>
Message-Id: <1459780549-12942-2-git-send-email-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
cpus.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/cpus.c b/cpus.c
index 8ae477728d..cbeb1f6139 100644
--- 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;
}