timer: Avoid integer overflows in usec and nsec calculations

When timer_calc_usec() is used with large timeout values, such as 60s,
the integer math can overflow and produce different results than when
using timer_calc(time / 1000) for the same timeout.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 31 insertions, 24 deletions

diff --git a/src/hw/timer.c b/src/hw/timer.c
index 03d22b2..bdcb3bf 100644
--- a/src/hw/timer.c
+++ b/src/hw/timer.c
@@ -159,6 +159,29 @@ timer_read(void)
     return timer_adjust_bits(v, 0xffff);
 }
 
+// Return the TSC value that is 'msecs' time in the future.
+u32
+timer_calc(u32 msecs)
+{
+    return timer_read() + (GET_GLOBAL(TimerKHz) * msecs);
+}
+u32
+timer_calc_usec(u32 usecs)
+{
+    u32 cur = timer_read(), khz = GET_GLOBAL(TimerKHz);
+    if (usecs > 500000)
+        return cur + DIV_ROUND_UP(usecs, 1000) * khz;
+    return cur + DIV_ROUND_UP(usecs * khz, 1000);
+}
+static u32
+timer_calc_nsec(u32 nsecs)
+{
+    u32 cur = timer_read(), khz = GET_GLOBAL(TimerKHz);
+    if (nsecs > 500000)
+        return cur + DIV_ROUND_UP(nsecs, 1000000) * khz;
+    return cur + DIV_ROUND_UP(nsecs * khz, 1000000);
+}
+
 // Check if the current time is past a previously calculated end time.
 int
 timer_check(u32 end)
@@ -167,53 +190,37 @@ timer_check(u32 end)
 }
 
 static void
-timer_delay(u32 diff)
+timer_delay(u32 end)
 {
-    u32 start = timer_read();
-    u32 end = start + diff;
     while (!timer_check(end))
         cpu_relax();
 }
 
 static void
-timer_sleep(u32 diff)
+timer_sleep(u32 end)
 {
-    u32 start = timer_read();
-    u32 end = start + diff;
     while (!timer_check(end))
         yield();
 }
 
 void ndelay(u32 count) {
-    timer_delay(DIV_ROUND_UP(count * GET_GLOBAL(TimerKHz), 1000000));
+    timer_delay(timer_calc_nsec(count));
 }
 void udelay(u32 count) {
-    timer_delay(DIV_ROUND_UP(count * GET_GLOBAL(TimerKHz), 1000));
+    timer_delay(timer_calc_usec(count));
 }
 void mdelay(u32 count) {
-    timer_delay(count * GET_GLOBAL(TimerKHz));
+    timer_delay(timer_calc(count));
 }
 
 void nsleep(u32 count) {
-    timer_sleep(DIV_ROUND_UP(count * GET_GLOBAL(TimerKHz), 1000000));
+    timer_sleep(timer_calc_nsec(count));
 }
 void usleep(u32 count) {
-    timer_sleep(DIV_ROUND_UP(count * GET_GLOBAL(TimerKHz), 1000));
+    timer_sleep(timer_calc_usec(count));
 }
 void msleep(u32 count) {
-    timer_sleep(count * GET_GLOBAL(TimerKHz));
-}
-
-// Return the TSC value that is 'msecs' time in the future.
-u32
-timer_calc(u32 msecs)
-{
-    return timer_read() + (GET_GLOBAL(TimerKHz) * msecs);
-}
-u32
-timer_calc_usec(u32 usecs)
-{
-    return timer_read() + DIV_ROUND_UP(GET_GLOBAL(TimerKHz) * usecs, 1000);
+    timer_sleep(timer_calc(count));
 }