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Commit 9da8f4e8 authored by Kevin Pedretti's avatar Kevin Pedretti Committed by Avi Kivity
Browse files

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: default avatarKevin Pedretti <kevin.pedretti@gmail.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent b33ac88b

drivers/kvm/lapic.c

+26 −10
Original line number Diff line number Diff line
@@ -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;