Commit 71760950bf3dc796e5e53ea3300dec724a09f593
("arm/arm64: KVM: add a common vgic_queue_irq_to_lr fn") introduced
vgic_queue_irq_to_lr() function with additional vgic_dist_irq_is_pending()
check before setting LR_STATE_PENDING bit. In some cases it started
causing the following situation if the userland quickly drops the IRQ back
to inactive state for some reason:
1. Userland injects an IRQ with level == 1, this ends up in
vgic_update_irq_pending(), which in turn calls vgic_dist_irq_set_pending()
for this IRQ.
2. vCPU gets kicked. But kernel does not manage to reschedule it quickly
(!!!)
3. Userland quickly resets the IRQ to level == 0. vgic_update_irq_pending()
in this case will call vgic_dist_irq_clear_pending() and reset the
pending flag.
4. vCPU finally wakes up. It succesfully rolls through through
__kvm_vgic_flush_hwstate(), which populates vGIC registers. However,
since neither pending nor active flags are now set for this IRQ,
vgic_queue_irq_to_lr() does not set any state bits on this LR at all.
Since this is level-sensitive IRQ, we end up in LR containing only
LR_EOI_INT bit, causing unnecessary immediate exit from the guest.
This patch fixes the problem by adding forgotten vgic_cpu_irq_clear().
This causes the IRQ not to be included into any lists, if it has been
picked up after getting dropped to inactive level. Since this is a
level-sensitive IRQ, this is correct behavior.
The bug was caught on ARM64 kernel v4.1.6, running qemu "virt" guest,
where it was caused by emulated pl011.
Signed-off-by: Pavel Fedin <p.fedin@xxxxxxxxxxx>
---
virt/kvm/arm/vgic.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
index 34dad3c..bf155e3 100644
--- a/virt/kvm/arm/vgic.c
+++ b/virt/kvm/arm/vgic.c
@@ -1111,7 +1111,8 @@ static void vgic_queue_irq_to_lr(struct kvm_vcpu *vcpu, int irq,
kvm_debug("Set active, clear distributor: 0x%x\n", vlr.state);
vgic_irq_clear_active(vcpu, irq);
vgic_update_state(vcpu->kvm);
- } else if (vgic_dist_irq_is_pending(vcpu, irq)) {
+ } else {
+ WARN_ON(!vgic_dist_irq_is_pending(vcpu, irq));
vlr.state |= LR_STATE_PENDING;
kvm_debug("Set pending: 0x%x\n", vlr.state);
}
@@ -1567,8 +1568,10 @@ static int vgic_update_irq_pending(struct kvm *kvm, int cpuid,
} else {
if (level_triggered) {
vgic_dist_irq_clear_level(vcpu, irq_num);
- if (!vgic_dist_irq_soft_pend(vcpu, irq_num))
+ if (!vgic_dist_irq_soft_pend(vcpu, irq_num)) {
vgic_dist_irq_clear_pending(vcpu, irq_num);
+ vgic_cpu_irq_clear(vcpu, irq_num);
+ }
}
ret = false;
--
2.4.4
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