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[RFC v4 08/10] KVM: arm/arm64: Set up a background timer for the physical timer emulation

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Set a background timer for the EL1 physical timer emulation while VMs
are running, so that VMs get the physical timer interrupts in a timely
manner.

Schedule the background timer on entry to the VM and cancel it on exit.
This would not have any performance impact to the guest OSes that
currently use the virtual timer since the physical timer is always not
enabled.

Signed-off-by: Jintack Lim <jintack@cs.columbia.edu>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
---
 virt/kvm/arm/arch_timer.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index 0ea7452..33257b5 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -229,6 +229,22 @@ static int kvm_timer_update_state(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+/* Schedule the background timer for the emulated timer. */
+static void kvm_timer_emulate(struct kvm_vcpu *vcpu,
+			      struct arch_timer_context *timer_ctx)
+{
+	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
+
+	if (kvm_timer_should_fire(timer_ctx))
+		return;
+
+	if (!kvm_timer_irq_can_fire(timer_ctx))
+		return;
+
+	/*  The timer has not yet expired, schedule a background timer */
+	timer_arm(timer, kvm_timer_compute_delta(timer_ctx));
+}
+
 /*
  * Schedule the background timer before calling kvm_vcpu_block, so that this
  * thread is removed from its waitqueue and made runnable when there's a timer
@@ -286,6 +302,9 @@ void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu)
 	if (kvm_timer_update_state(vcpu))
 		return;
 
+	/* Set the background timer for the physical timer emulation. */
+	kvm_timer_emulate(vcpu, vcpu_ptimer(vcpu));
+
 	/*
 	* If we enter the guest with the virtual input level to the VGIC
 	* asserted, then we have already told the VGIC what we need to, and
@@ -348,7 +367,11 @@ void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu)
 {
 	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
 
-	BUG_ON(timer_is_armed(timer));
+	/*
+	 * This is to cancel the background timer for the physical timer
+	 * emulation if it is set.
+	 */
+	timer_disarm(timer);
 
 	/*
 	 * The guest could have modified the timer registers or the timer
-- 
1.9.1

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[RFC v4 00/10] Provide the EL1 physical timer to the VM Jintack Lim <jintack@cs.columbia.edu> - 2017-02-03 16:30 +0100
  [RFC v4 09/10] KVM: arm64: Add the EL1 physical timer access handler Jintack Lim <jintack@cs.columbia.edu> - 2017-02-03 16:30 +0100
  [RFC v4 08/10] KVM: arm/arm64: Set up a background timer for the physical timer emulation Jintack Lim <jintack@cs.columbia.edu> - 2017-02-03 16:30 +0100
  [RFC v4 10/10] KVM: arm/arm64: Emulate the EL1 phys timer registers Jintack Lim <jintack@cs.columbia.edu> - 2017-02-03 16:30 +0100
  Re: [RFC v4 00/10] Provide the EL1 physical timer to the VM Marc Zyngier <marc.zyngier@arm.com> - 2017-02-03 17:20 +0100
    Re: [RFC v4 00/10] Provide the EL1 physical timer to the VM Jintack Lim <jintack@cs.columbia.edu> - 2017-02-03 18:00 +0100
      Re: [RFC v4 00/10] Provide the EL1 physical timer to the VM Marc Zyngier <marc.zyngier@arm.com> - 2017-02-03 18:00 +0100

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