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KVM: Improve local apic timer wraparound handling 

Better handle wrap-around cases when reading the APIC CCR
(current count register).  Also, if ICR is 0, CCR should also
be 0... previously reading CCR before setting ICR would result
in a large kinda-random number.

Signed-off-by: Kevin Pedretti <kevin.pedretti@gmail.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Kevin Pedretti 2007-10-21 08:55:50 +02:00 committed by Avi Kivity
parent b33ac88b4c
commit 9da8f4e83a
1 changed files with 26 additions and 10 deletions
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36
drivers/kvm/lapic.c
View File

@ -494,12 +494,19 @@ static void apic_send_ipi(struct kvm_lapic *apic)
static u32 apic_get_tmcct(struct kvm_lapic *apic)
{
u32 counter_passed;
ktime_t passed, now = apic->timer.dev.base->get_time();
u32 tmcct = apic_get_reg(apic, APIC_TMICT);
u64 counter_passed;
ktime_t passed, now;
u32 tmcct;
ASSERT(apic != NULL);
now = apic->timer.dev.base->get_time();
tmcct = apic_get_reg(apic, APIC_TMICT);
/* if initial count is 0, current count should also be 0 */
if (tmcct == 0)
return 0;
if (unlikely(ktime_to_ns(now) <=
ktime_to_ns(apic->timer.last_update))) {
/* Wrap around */
@ -514,15 +521,24 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
counter_passed = div64_64(ktime_to_ns(passed),
(APIC_BUS_CYCLE_NS * apic->timer.divide_count));
tmcct -= counter_passed;
if (tmcct <= 0) {
if (unlikely(!apic_lvtt_period(apic)))
if (counter_passed > tmcct) {
if (unlikely(!apic_lvtt_period(apic))) {
/* one-shot timers stick at 0 until reset */
tmcct = 0;
else
do {
tmcct += apic_get_reg(apic, APIC_TMICT);
} while (tmcct <= 0);
} else {
/*
* periodic timers reset to APIC_TMICT when they
* hit 0. The while loop simulates this happening N
* times. (counter_passed %= tmcct) would also work,
* but might be slower or not work on 32-bit??
*/
while (counter_passed > tmcct)
counter_passed -= tmcct;
tmcct -= counter_passed;
}
} else {
tmcct -= counter_passed;
}
return tmcct;