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

[Mark Cave-Ayland]

On 10/05/17 09:57, 李林 wrote:

>   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);
> 

Adding Gerd as USB maintainer to CC.


ATB,

Mark.