[PATCH] KVM: arm64: vgic: Fix soft lockup during VM teardown

[Shanker Donthineni <sdonthineni@nvidia.com>]

Getting intermittent CPU soft lockups during the virtual machines
teardown on a system with GICv4 features enabled. The function
__synchronize_hardirq() has been waiting for IRQD_IRQ_INPROGRESS
to be cleared forever as per the current implementation.

CPU stuck here for a long time leads to soft lockup:
  while (irqd_irq_inprogress(&desc->irq_data))
	cpu_relax();

Call trace from the lockup CPU:
 [   87.238866] watchdog: BUG: soft lockup - CPU#37 stuck for 23s!
 [   87.250025] CPU: 37 PID: 1031 Comm: qemu-system-aarch64
 [   87.358397] Call trace:
 [   87.360891]  __synchronize_hardirq+0x48/0x140
 [   87.365343]  free_irq+0x138/0x424
 [   87.368727]  vgic_v4_teardown+0xa4/0xe0
 [   87.372649]  __kvm_vgic_destroy+0x18c/0x194
 [   87.376922]  kvm_vgic_destroy+0x28/0x3c
 [   87.380839]  kvm_arch_destroy_vm+0x24/0x44
 [   87.385024]  kvm_destroy_vm+0x158/0x2c4
 [   87.388943]  kvm_vm_release+0x6c/0x98
 [   87.392681]  __fput+0x70/0x220
 [   87.395800]  ____fput+0x10/0x20
 [   87.399005]  task_work_run+0xb4/0x23c
 [   87.402746]  do_exit+0x2bc/0x8a4
 [   87.406042]  do_group_exit+0x34/0xb0
 [   87.409693]  get_signal+0x878/0x8a0
 [   87.413254]  do_notify_resume+0x138/0x1530
 [   87.417440]  el0_svc+0xdc/0xf0
 [   87.420559]  el0t_64_sync_handler+0xf0/0x11c
 [   87.424919]  el0t_64_sync+0x18c/0x190

The state of the IRQD_IRQ_INPROGRESS information is lost inside
irq_domain_activate_irq() which happens before calling free_irq().
Instrumented the code and confirmed, the IRQD state is changed from
0x10401400 to 0x10441600 instead of 0x10401600 causing problem.

Call trace from irqd_set_activated():
 [   78.983544] irqd_set_activated: lost IRQD_IRQ_INPROGRESS
                old=0x10401400, new=0x10441600
 [   78.992093] CPU: 19 PID: 1511 Comm: qemu-system-aarch64
 [   79.008461] Call trace:
 [   79.010956]  dump_backtrace.part.0+0xc8/0xe0
 [   79.015328]  show_stack+0x18/0x54
 [   79.018713]  dump_stack_lvl+0x64/0x7c
 [   79.022459]  dump_stack+0x18/0x30
 [   79.025842]  irq_domain_activate_irq+0x88/0x94
 [   79.030385]  vgic_v3_save_pending_tables+0x260/0x29c
 [   79.035463]  vgic_set_common_attr+0xac/0x23c
 [   79.039826]  vgic_v3_set_attr+0x48/0x60
 [   79.043742]  kvm_device_ioctl+0x120/0x19c
 [   79.047840]  __arm64_sys_ioctl+0x42c/0xe00
 [   79.052027]  invoke_syscall.constprop.0+0x50/0xe0
 [   79.056835]  do_el0_svc+0x58/0x180
 [   79.060308]  el0_svc+0x38/0xf0
 [   79.063425]  el0t_64_sync_handler+0xf0/0x11c
 [   79.067785]  el0t_64_sync+0x18c/0x190

irqreturn_t handle_irq_event(struct irq_desc *desc)
{
    irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS);
    raw_spin_unlock(&desc->lock);

    ret = handle_irq_event_percpu(desc);

    raw_spin_lock(&desc->lock);
    irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);
}

In this particular failed case and based on traces, the two functions
irqd_set_activated() and handle_irq_event() are concurrently modifying
IRQD state without both holding desc->lock. The irqd_set_activated()
execution path is reading memory 'state_use_accessors' in between set
& clear of IRQD_IRQ_INPROGRESS state change and writing the modified
data after executing 'irqd_clear(desc->irq_data, IRQD_IRQ_INPROGRESS)'.

To fix the lockup issue, hold desc->lock when calling functions
irq_domain_activate_irq() and irq_domain_deactivate_irq).

Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
---
 arch/arm64/kvm/vgic/vgic-v3.c | 6 ++++++
 arch/arm64/kvm/vgic/vgic-v4.c | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
index 2074521d4a8c..e6aa909fcbe2 100644
--- a/arch/arm64/kvm/vgic/vgic-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-v3.c
@@ -353,22 +353,28 @@ int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq)
 static void unmap_all_vpes(struct vgic_dist *dist)
 {
 	struct irq_desc *desc;
+	unsigned long flags;
 	int i;
 
 	for (i = 0; i < dist->its_vm.nr_vpes; i++) {
 		desc = irq_to_desc(dist->its_vm.vpes[i]->irq);
+		raw_spin_lock_irqsave(&desc->lock, flags);
 		irq_domain_deactivate_irq(irq_desc_get_irq_data(desc));
+		raw_spin_unlock_irqrestore(&desc->lock, flags);
 	}
 }
 
 static void map_all_vpes(struct vgic_dist *dist)
 {
 	struct irq_desc *desc;
+	unsigned long flags;
 	int i;
 
 	for (i = 0; i < dist->its_vm.nr_vpes; i++) {
 		desc = irq_to_desc(dist->its_vm.vpes[i]->irq);
+		raw_spin_lock_irqsave(&desc->lock, flags);
 		irq_domain_activate_irq(irq_desc_get_irq_data(desc), false);
+		raw_spin_unlock_irqrestore(&desc->lock, flags);
 	}
 }
 
diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index ad06ba6c9b00..a01b8313e82c 100644
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c
@@ -139,8 +139,10 @@ static void vgic_v4_enable_vsgis(struct kvm_vcpu *vcpu)
 		/* Transfer the full irq state to the vPE */
 		vgic_v4_sync_sgi_config(vpe, irq);
 		desc = irq_to_desc(irq->host_irq);
+		raw_spin_lock(&desc->lock);
 		ret = irq_domain_activate_irq(irq_desc_get_irq_data(desc),
 					      false);
+		raw_spin_unlock(&desc->lock);
 		if (!WARN_ON(ret)) {
 			/* Transfer pending state */
 			ret = irq_set_irqchip_state(irq->host_irq,
@@ -177,7 +179,9 @@ static void vgic_v4_disable_vsgis(struct kvm_vcpu *vcpu)
 		WARN_ON(ret);
 
 		desc = irq_to_desc(irq->host_irq);
+		raw_spin_lock(&desc->lock);
 		irq_domain_deactivate_irq(irq_desc_get_irq_data(desc));
+		raw_spin_unlock(&desc->lock);
 	unlock:
 		raw_spin_unlock_irqrestore(&irq->irq_lock, flags);
 		vgic_put_irq(vcpu->kvm, irq);
-- 
2.25.1