arm/arm64: KVM: Keep elrsr/aisr in sync with software model

commit ae705930 upstream.

There is an interesting bug in the vgic code, which manifests itself
when the KVM run loop has a signal pending or needs a vmid generation
rollover after having disabled interrupts but before actually switching
to the guest.

In this case, we flush the vgic as usual, but we sync back the vgic
state and exit to userspace before entering the guest.  The consequence
is that we will be syncing the list registers back to the software model
using the GICH_ELRSR and GICH_EISR from the last execution of the guest,
potentially overwriting a list register containing an interrupt.

This showed up during migration testing where we would capture a state
where the VM has masked the arch timer but there were no interrupts,
resulting in a hung test.

Cc: Marc Zyngier <marc.zyngier@arm.com>
Reported-by: Alex Bennee <alex.bennee@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
[ luis: backported to 3.16: used shannon's backport to 3.14 ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

virt/kvm/arm/vgic.c

@@ -1042,6 +1042,7 @@ static bool vgic_queue_irq(struct kvm_vcpu *vcpu, u8 sgi_source_id, int irq)
 			  lr, irq, vgic_cpu->vgic_lr[lr]);
 		BUG_ON(!test_bit(lr, vgic_cpu->lr_used));
 		vgic_cpu->vgic_lr[lr] |= GICH_LR_PENDING_BIT;
+		__clear_bit(lr, (unsigned long *)vgic_cpu->vgic_elrsr);
 		return true;
 	}
 
@@ -1055,6 +1056,7 @@ static bool vgic_queue_irq(struct kvm_vcpu *vcpu, u8 sgi_source_id, int irq)
 	vgic_cpu->vgic_lr[lr] = MK_LR_PEND(sgi_source_id, irq);
 	vgic_cpu->vgic_irq_lr_map[irq] = lr;
 	set_bit(lr, vgic_cpu->lr_used);
+	__clear_bit(lr, (unsigned long *)vgic_cpu->vgic_elrsr);
 
 	if (!vgic_irq_is_edge(vcpu, irq))
 		vgic_cpu->vgic_lr[lr] |= GICH_LR_EOI;
@@ -1209,6 +1211,14 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
 	if (vgic_cpu->vgic_misr & GICH_MISR_U)
 		vgic_cpu->vgic_hcr &= ~GICH_HCR_UIE;
 
+	/*
+	 * In the next iterations of the vcpu loop, if we sync the vgic state
+	 * after flushing it, but before entering the guest (this happens for
+	 * pending signals and vmid rollovers), then make sure we don't pick
+	 * up any old maintenance interrupts here.
+	 */
+	memset(vgic_cpu->vgic_eisr, 0, sizeof(vgic_cpu->vgic_eisr[0]) * 2);
+
 	return level_pending;
 }