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Commit 9bc5791d authored by Jan Kiszka's avatar Jan Kiszka Committed by Avi Kivity
Browse files

KVM: x86: Add module parameter for lapic periodic timer limit 



Certain guests, specifically RTOSes, request faster periodic timers than
what we allow by default. Add a module parameter to adjust the limit for
non-standard setups. Also add a rate-limited warning in case the guest
requested more.

Signed-off-by: default avatarJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent bd80158a

arch/x86/kvm/lapic.c

+13 −2
Original line number Diff line number Diff line
@@ -68,6 +68,9 @@ 
#define VEC_POS(v) ((v) & (32 - 1))

#define REG_POS(v) (((v) >> 5) << 4)



static unsigned int min_timer_period_us = 500;

module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);



static inline u32 apic_get_reg(struct kvm_lapic *apic, int reg_off)

{

	return *((u32 *) (apic->regs + reg_off));
@@ -677,8 +680,16 @@ static void start_apic_timer(struct kvm_lapic *apic) 
	 * scheduler.

	 */

	if (apic_lvtt_period(apic)) {

		if (apic->lapic_timer.period < NSEC_PER_MSEC/2)

			apic->lapic_timer.period = NSEC_PER_MSEC/2;

		s64 min_period = min_timer_period_us * 1000LL;



		if (apic->lapic_timer.period < min_period) {

			pr_info_ratelimited(

				"kvm: vcpu %i: requested %lld ns "

				"lapic timer period limited to %lld ns\n",

				apic->vcpu->vcpu_id, apic->lapic_timer.period,

				min_period);

			apic->lapic_timer.period = min_period;

		}

	}



	hrtimer_start(&apic->lapic_timer.timer,