[Qemu-devel] ehci: fix "int" overflow for calculation ehci->last_run_ns

[李林]

  If we experience large delays between echi timer callbacks (i.e. because 
other periodic handlers have taken a lot of time to complete) we get a lot of 
skipped frames which then delay ehci timer callback.
 Then we will calculation  ehci->last_run_ns,but skipped_uframes is int,so 
"UFRAME_TIMER_NS * skipped_uframes" will be int,and if skipped_uframes is big 
enough ,it can overflow ,and this can not calculation the right number,then it 
can   raise  large amountsinterrupts;
  Observable behaviour is qemu consuming 100% host CPU time while guest is 
unresponsive. This misbehavior could happen for a while and QEMU does not get 
out from this state automatically without the patch in Branch-master repository.


diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
index 50ef817f93..8df2f08783 100644
--- a/hw/usb/hcd-ehci.c
+++ b/hw/usb/hcd-ehci.c
@@ -2238,7 +2238,7 @@ static void ehci_frame_timer(void *opaque)
     int need_timer = 0;
     int64_t expire_time, t_now;
     uint64_t ns_elapsed;
-    int uframes, skipped_uframes;
+    uint64 uframes, skipped_uframes;
     int i;


     t_now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);