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Commit accb99bc authored by Christoffer Dall's avatar Christoffer Dall Committed by Marc Zyngier
Browse files

KVM: arm/arm64: Simplify bg_timer programming 



Instead of calling into kvm_timer_[un]schedule from the main kvm
blocking path, test if the VCPU is on the wait queue from the load/put
path and perform the background timer setup/cancel in this path.

This has the distinct advantage that we no longer race between load/put
and schedule/unschedule and programming and canceling of the bg_timer
always happens when the timer state is not loaded.

Note that we must now remove the checks in kvm_timer_blocking that do
not schedule a background timer if one of the timers can fire, because
we no longer have a guarantee that kvm_vcpu_check_block() will be called
before kvm_timer_blocking.

Reported-by: default avatarAndre Przywara <andre.przywara@arm.com>
Signed-off-by: default avatarChristoffer Dall <christoffer.dall@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent e329fb75

include/kvm/arm_arch_timer.h

+0 −3
Original line number Diff line number Diff line
@@ -76,9 +76,6 @@ int kvm_arm_timer_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr); 


bool kvm_timer_is_pending(struct kvm_vcpu *vcpu);



void kvm_timer_schedule(struct kvm_vcpu *vcpu);

void kvm_timer_unschedule(struct kvm_vcpu *vcpu);



u64 kvm_phys_timer_read(void);



void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu);

virt/kvm/arm/arch_timer.c

+14 −21
Original line number Diff line number Diff line
@@ -349,22 +349,12 @@ static void vtimer_save_state(struct kvm_vcpu *vcpu) 
 * thread is removed from its waitqueue and made runnable when there's a timer

 * interrupt to handle.

 */

void kvm_timer_schedule(struct kvm_vcpu *vcpu)

static void kvm_timer_blocking(struct kvm_vcpu *vcpu)

{

	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;

	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);

	struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);



	vtimer_save_state(vcpu);



	/*

	 * No need to schedule a background timer if any guest timer has

	 * already expired, because kvm_vcpu_block will return before putting

	 * the thread to sleep.

	 */

	if (kvm_timer_should_fire(vtimer) || kvm_timer_should_fire(ptimer))

		return;



	/*

	 * If both timers are not capable of raising interrupts (disabled or

	 * masked), then there's no more work for us to do.
@@ -373,12 +363,19 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu) 
		return;



	/*

	 * The guest timers have not yet expired, schedule a background timer.

	 * At least one guest time will expire. Schedule a background timer.

	 * Set the earliest expiration time among the guest timers.

	 */

	soft_timer_start(&timer->bg_timer, kvm_timer_earliest_exp(vcpu));

}



static void kvm_timer_unblocking(struct kvm_vcpu *vcpu)

{

	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;



	soft_timer_cancel(&timer->bg_timer);

}



static void vtimer_restore_state(struct kvm_vcpu *vcpu)

{

	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
@@ -401,15 +398,6 @@ static void vtimer_restore_state(struct kvm_vcpu *vcpu) 
	local_irq_restore(flags);

}



void kvm_timer_unschedule(struct kvm_vcpu *vcpu)

{

	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;



	vtimer_restore_state(vcpu);



	soft_timer_cancel(&timer->bg_timer);

}



static void set_cntvoff(u64 cntvoff)

{

	u32 low = lower_32_bits(cntvoff);
@@ -485,6 +473,8 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu) 
	/* Set the background timer for the physical timer emulation. */

	phys_timer_emulate(vcpu);



	kvm_timer_unblocking(vcpu);



	/* If the timer fired while we weren't running, inject it now */

	if (kvm_timer_should_fire(ptimer) != ptimer->irq.level)

		kvm_timer_update_irq(vcpu, !ptimer->irq.level, ptimer);
@@ -527,6 +517,9 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu) 
	 */

	soft_timer_cancel(&timer->phys_timer);



	if (swait_active(kvm_arch_vcpu_wq(vcpu)))

		kvm_timer_blocking(vcpu);



	/*

	 * The kernel may decide to run userspace after calling vcpu_put, so

	 * we reset cntvoff to 0 to ensure a consistent read between user

virt/kvm/arm/arm.c

+0 −2
Original line number Diff line number Diff line
@@ -335,13 +335,11 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu) 


void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)

{

	kvm_timer_schedule(vcpu);

	kvm_vgic_v4_enable_doorbell(vcpu);

}



void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)

{

	kvm_timer_unschedule(vcpu);

	kvm_vgic_v4_disable_doorbell(vcpu);

}