[Qemu-devel] [PATCH v2 11/21] aspeed/timer: Ensure positive muldiv delta

["Cédric Le Goater" <clg@kaod.org>]

From: Christian Svensson <bluecmd@google.com>

If the host decrements the counter register that results in a negative
delta. This is then passed to muldiv64 which only handles unsigned
numbers resulting in bogus results.

This fix ensures the delta being operated on is positive.

Test case: kexec a kernel using aspeed_timer and it will freeze on the
second bootup when the kernel initializes the timer. With this patch
that no longer happens and the timer appears to run OK.

Signed-off-by: Christian Svensson <bluecmd@google.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 hw/timer/aspeed_timer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/timer/aspeed_timer.c b/hw/timer/aspeed_timer.c
index 6501fa0768e7..1f0f1886fb2a 100644
--- a/hw/timer/aspeed_timer.c
+++ b/hw/timer/aspeed_timer.c
@@ -275,7 +275,11 @@ static void aspeed_timer_set_value(AspeedTimerCtrlState *s, int timer, int reg,
             int64_t delta = (int64_t) value - (int64_t) calculate_ticks(t, now);
             uint32_t rate = calculate_rate(t);
 
-            t->start += muldiv64(delta, NANOSECONDS_PER_SECOND, rate);
+            if (delta >= 0) {
+                t->start += muldiv64(delta, NANOSECONDS_PER_SECOND, rate);
+            } else {
+                t->start -= muldiv64(-delta, NANOSECONDS_PER_SECOND, rate);
+            }
             aspeed_timer_mod(t);
         }
         break;
-- 
2.21.0