[Qemu-devel] [PATCH v3] timer: a9gtimer: remove loop to auto-increment comparator

[Qemu-devel] [PATCH v3] timer: a9gtimer: remove loop to auto-increment comparator

[P J P]

From: Prasad J Pandit <pjp@fedoraproject.org>

ARM A9MP processor has a peripheral timer with an auto-increment
register, which holds an increment step value. A user could set
this value to zero. When auto-increment control bit is enabled,
it leads to an infinite loop in 'a9_gtimer_update' while
updating comparator value. Remove this loop incrementing the
comparator value.

Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/timer/a9gtimer.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

Update per:
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg00079.html

diff --git a/hw/timer/a9gtimer.c b/hw/timer/a9gtimer.c
index 772f85f..add2f31 100644
--- a/hw/timer/a9gtimer.c
+++ b/hw/timer/a9gtimer.c
@@ -73,6 +73,7 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
 
     A9GTimerUpdate update = a9_gtimer_get_update(s);
     int i;
+    uint64_t inc;
     int64_t next_cdiff = 0;
 
     for (i = 0; i < s->num_cpu; ++i) {
@@ -82,16 +83,15 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
         if ((s->control & R_CONTROL_TIMER_ENABLE) &&
                 (gtb->control & R_CONTROL_COMP_ENABLE)) {
             /* R2p0+, where the compare function is >= */
-            while (gtb->compare < update.new) {
+            if (gtb->compare < update.new
+                && gtb->control & R_CONTROL_AUTO_INCREMENT) {
                 DB_PRINT("Compare event happened for CPU %d\n", i);
                 gtb->status = 1;
-                if (gtb->control & R_CONTROL_AUTO_INCREMENT) {
-                    DB_PRINT("Auto incrementing timer compare by %" PRId32 "\n",
-                             gtb->inc);
-                    gtb->compare += gtb->inc;
-                } else {
-                    break;
-                }
+                inc = update.new - gtb->compare - 1;
+                inc = gtb->inc ? QEMU_ALIGN_DOWN(inc, gtb->inc) : 0;
+                DB_PRINT("Auto incrementing timer compare by %"
+                                                    PRId64 "\n", inc);
+                gtb->compare += inc;
             }
             cdiff = (int64_t)gtb->compare - (int64_t)update.new + 1;
             if (cdiff > 0 && (cdiff < next_cdiff || !next_cdiff)) {
-- 
2.5.5

Re: [Qemu-devel] [PATCH v3] timer: a9gtimer: remove loop to auto-increment comparator

[Peter Maydell]

On 3 October 2016 at 10:04, P J P <ppandit@redhat.com> wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> ARM A9MP processor has a peripheral timer with an auto-increment
> register, which holds an increment step value. A user could set
> this value to zero. When auto-increment control bit is enabled,
> it leads to an infinite loop in 'a9_gtimer_update' while
> updating comparator value. Remove this loop incrementing the
> comparator value.
>
> Reported-by: Li Qiang <liqiang6-s@360.cn>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/timer/a9gtimer.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> Update per:
>   -> https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg00079.html
>
> diff --git a/hw/timer/a9gtimer.c b/hw/timer/a9gtimer.c
> index 772f85f..add2f31 100644
> --- a/hw/timer/a9gtimer.c
> +++ b/hw/timer/a9gtimer.c
> @@ -73,6 +73,7 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
>
>      A9GTimerUpdate update = a9_gtimer_get_update(s);
>      int i;
> +    uint64_t inc;
>      int64_t next_cdiff = 0;
>
>      for (i = 0; i < s->num_cpu; ++i) {
> @@ -82,16 +83,15 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
>          if ((s->control & R_CONTROL_TIMER_ENABLE) &&
>                  (gtb->control & R_CONTROL_COMP_ENABLE)) {
>              /* R2p0+, where the compare function is >= */
> -            while (gtb->compare < update.new) {
> +            if (gtb->compare < update.new
> +                && gtb->control & R_CONTROL_AUTO_INCREMENT) {
>                  DB_PRINT("Compare event happened for CPU %d\n", i);
>                  gtb->status = 1;
> -                if (gtb->control & R_CONTROL_AUTO_INCREMENT) {
> -                    DB_PRINT("Auto incrementing timer compare by %" PRId32 "\n",
> -                             gtb->inc);
> -                    gtb->compare += gtb->inc;
> -                } else {
> -                    break;
> -                }
> +                inc = update.new - gtb->compare - 1;
> +                inc = gtb->inc ? QEMU_ALIGN_DOWN(inc, gtb->inc) : 0;
> +                DB_PRINT("Auto incrementing timer compare by %"
> +                                                    PRId64 "\n", inc);
> +                gtb->compare += inc;
>              }
>              cdiff = (int64_t)gtb->compare - (int64_t)update.new + 1;
>              if (cdiff > 0 && (cdiff < next_cdiff || !next_cdiff)) {

This is still losing the setting of gtb->status in the
case where the auto-increment bit is not set.

thanks
-- PMM

Re: [Qemu-devel] [PATCH v3] timer: a9gtimer: remove loop to auto-increment comparator

[P J P]

+-- On Fri, 7 Oct 2016, Peter Maydell wrote --+
| This is still losing the setting of gtb->status in the
| case where the auto-increment bit is not set.

Ah, I've sent a revised patch v4. Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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