[Xen-devel] [PATCH][HVM] fix multiplication overflow in hvm/pmtimer.c

[Kouya Shimura <kouya@xxxxxxxxxxxxxx>]

Hi,

Too many ACPI events (SCI) are raised on hvm because of
multiplication overflow.

FREQUENCE_PMTIMER=3579545
(1000000000ULL << 32) / FREQUENCE_PMTIMER = 0xae9a7b1663a
pmt_cycles_until_flip =~ 0x80000000
0xae9a7b1663a*0x80000000 = overflow!!!

Thanks,
Kouya

Signed-off-by: Kouya Shimura <kouya@xxxxxxxxxxxxxx>

diff -r 80eb95dc0dd9 xen/arch/x86/hvm/pmtimer.c
--- a/xen/arch/x86/hvm/pmtimer.c        Thu Jun 14 18:01:42 2007 +0100
+++ b/xen/arch/x86/hvm/pmtimer.c        Fri Jun 15 11:46:36 2007 +0900
@@ -97,10 +97,10 @@ static void pmt_timer_callback(void *opa
     pmt_cycles_until_flip = TMR_VAL_MSB - (s->pm.tmr_val & (TMR_VAL_MSB - 1));
     
     /* Overall time between MSB flips */
-    time_until_flip = (1000000000ULL << 31) / FREQUENCE_PMTIMER;
+    time_until_flip = (1000000000ULL << 23) / FREQUENCE_PMTIMER;
     
     /* Reduced appropriately */
-    time_until_flip = (time_until_flip * pmt_cycles_until_flip) / (1ULL<<31);
+    time_until_flip = (time_until_flip * pmt_cycles_until_flip) >> 23;
     
     /* Wake up again near the next bit-flip */
     set_timer(&s->timer, NOW() + time_until_flip + MILLISECS(1));

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