[PATCH v3] eventdev/timer: fix overflow issue

[Erik Gabriel Carrillo]

The software timer adapter converts event timer timeout ticks to a
number of TSC cycles at which an rte_timer should expire. The
computation uses an integer multiplication that can result in overflow.

If necessary, reduce the timeout_nsecs value by the number of whole
seconds it contains to keep the value of the multiplier within a
range that will not result in overflow.  Add the saved value back later
to get the final result. Also, move the logic that checks the timeout
range into the function that performs the above computation.

Fixes: 6750b21bd6af ("eventdev: add default software timer adapter")
Cc: stable at dpdk.org

Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo at intel.com>
---
v3:
* Use integer operations instead of floating point, and use
  rte_reciprocal_divide() for division.

v2:
* Fix implicit int to float conversion build warning on Clang

 lib/eventdev/rte_event_timer_adapter.c | 97 ++++++++++++++++----------
 1 file changed, 59 insertions(+), 38 deletions(-)

diff --git a/lib/eventdev/rte_event_timer_adapter.c b/lib/eventdev/rte_event_timer_adapter.c
index 7f4f347369..23eb1d4a7d 100644
--- a/lib/eventdev/rte_event_timer_adapter.c
+++ b/lib/eventdev/rte_event_timer_adapter.c
@@ -18,6 +18,7 @@
 #include <rte_timer.h>
 #include <rte_service_component.h>
 #include <rte_telemetry.h>
+#include <rte_reciprocal.h>
 
 #include "event_timer_adapter_pmd.h"
 #include "eventdev_pmd.h"
@@ -734,13 +735,51 @@ swtim_callback(struct rte_timer *tim)
 	}
 }
 
-static __rte_always_inline uint64_t
+static __rte_always_inline int
 get_timeout_cycles(struct rte_event_timer *evtim,
-		   const struct rte_event_timer_adapter *adapter)
+		   const struct rte_event_timer_adapter *adapter,
+		   uint64_t *timeout_cycles)
 {
-	struct swtim *sw = swtim_pmd_priv(adapter);
-	uint64_t timeout_ns = evtim->timeout_ticks * sw->timer_tick_ns;
-	return timeout_ns * rte_get_timer_hz() / NSECPERSEC;
+	static struct rte_reciprocal_u64 nsecpersec_inverse;
+	static uint64_t timer_hz;
+	uint64_t rem_cycles, secs_cycles = 0;
+	uint64_t secs, timeout_nsecs;
+	uint64_t nsecpersec;
+	struct swtim *sw;
+
+	sw = swtim_pmd_priv(adapter);
+	nsecpersec = (uint64_t)NSECPERSEC;
+
+	timeout_nsecs = evtim->timeout_ticks * sw->timer_tick_ns;
+	if (timeout_nsecs > sw->max_tmo_ns)
+		return -1;
+	if (timeout_nsecs < sw->timer_tick_ns)
+		return -2;
+
+	/* Set these values in the first invocation */
+	if (!timer_hz) {
+		timer_hz = rte_get_timer_hz();
+		nsecpersec_inverse = rte_reciprocal_value_u64(nsecpersec);
+	}
+
+	/* If timeout_nsecs > nsecpersec, decrease timeout_nsecs by the number
+	 * of whole seconds it contains and convert that value to a number
+	 * of cycles. This keeps timeout_nsecs in the interval [0..nsecpersec)
+	 * in order to avoid overflow when we later multiply by timer_hz.
+	 */
+	if (timeout_nsecs > nsecpersec) {
+		secs = rte_reciprocal_divide_u64(timeout_nsecs,
+						 &nsecpersec_inverse);
+		secs_cycles = secs * timer_hz;
+		timeout_nsecs -= secs * nsecpersec;
+	}
+
+	rem_cycles = rte_reciprocal_divide_u64(timeout_nsecs * timer_hz,
+					       &nsecpersec_inverse);
+
+	*timeout_cycles = secs_cycles + rem_cycles;
+
+	return 0;
 }
 
 /* This function returns true if one or more (adapter) ticks have occurred since
@@ -774,23 +813,6 @@ swtim_did_tick(struct swtim *sw)
 	return false;
 }
 
-/* Check that event timer timeout value is in range */
-static __rte_always_inline int
-check_timeout(struct rte_event_timer *evtim,
-	      const struct rte_event_timer_adapter *adapter)
-{
-	uint64_t tmo_nsec;
-	struct swtim *sw = swtim_pmd_priv(adapter);
-
-	tmo_nsec = evtim->timeout_ticks * sw->timer_tick_ns;
-	if (tmo_nsec > sw->max_tmo_ns)
-		return -1;
-	if (tmo_nsec < sw->timer_tick_ns)
-		return -2;
-
-	return 0;
-}
-
 /* Check that event timer event queue sched type matches destination event queue
  * sched type
  */
@@ -1210,21 +1232,6 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter,
 			break;
 		}
 
-		ret = check_timeout(evtims[i], adapter);
-		if (unlikely(ret == -1)) {
-			__atomic_store_n(&evtims[i]->state,
-					RTE_EVENT_TIMER_ERROR_TOOLATE,
-					__ATOMIC_RELAXED);
-			rte_errno = EINVAL;
-			break;
-		} else if (unlikely(ret == -2)) {
-			__atomic_store_n(&evtims[i]->state,
-					RTE_EVENT_TIMER_ERROR_TOOEARLY,
-					__ATOMIC_RELAXED);
-			rte_errno = EINVAL;
-			break;
-		}
-
 		if (unlikely(check_destination_event_queue(evtims[i],
 							   adapter) < 0)) {
 			__atomic_store_n(&evtims[i]->state,
@@ -1240,7 +1247,21 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter,
 		evtims[i]->impl_opaque[0] = (uintptr_t)tim;
 		evtims[i]->impl_opaque[1] = (uintptr_t)adapter;
 
-		cycles = get_timeout_cycles(evtims[i], adapter);
+		ret = get_timeout_cycles(evtims[i], adapter, &cycles);
+		if (unlikely(ret == -1)) {
+			__atomic_store_n(&evtims[i]->state,
+					RTE_EVENT_TIMER_ERROR_TOOLATE,
+					__ATOMIC_RELAXED);
+			rte_errno = EINVAL;
+			break;
+		} else if (unlikely(ret == -2)) {
+			__atomic_store_n(&evtims[i]->state,
+					RTE_EVENT_TIMER_ERROR_TOOEARLY,
+					__ATOMIC_RELAXED);
+			rte_errno = EINVAL;
+			break;
+		}
+
 		ret = rte_timer_alt_reset(sw->timer_data_id, tim, cycles,
 					  type, lcore_id, NULL, evtims[i]);
 		if (ret < 0) {
-- 
2.23.0