KVM: arm64: vgic-its: Get rid of the lpi_list_lock

The last genuine use case for the lpi_list_lock was the global LPI
translation cache, which has been removed in favor of a per-ITS xarray.
Remove a layer from the locking puzzle by getting rid of it.

vgic_add_lpi() still has a critical section that needs to protect
against the insertion of other LPIs; change it to take the LPI xarray's
xa_lock to retain this property.
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240422200158.2606761-13-oliver.upton@linux.devSigned-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/vgic/vgic-init.c

@@ -53,7 +53,6 @@ void kvm_vgic_early_init(struct kvm *kvm)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
 
-	raw_spin_lock_init(&dist->lpi_list_lock);
 	xa_init_flags(&dist->lpi_xa, XA_FLAGS_LOCK_IRQ);
 }
 

arch/arm64/kvm/vgic/vgic-its.c

@@ -69,7 +69,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
 	irq->target_vcpu = vcpu;
 	irq->group = 1;
 
-	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
+	xa_lock_irqsave(&dist->lpi_xa, flags);
 
 	/*
 	 * There could be a race with another vgic_add_lpi(), so we need to
@@ -84,14 +84,14 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
 		goto out_unlock;
 	}
 
-	ret = xa_err(xa_store(&dist->lpi_xa, intid, irq, 0));
+	ret = xa_err(__xa_store(&dist->lpi_xa, intid, irq, 0));
 	if (ret) {
 		xa_release(&dist->lpi_xa, intid);
 		kfree(irq);
 	}
 
 out_unlock:
-	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
+	xa_unlock_irqrestore(&dist->lpi_xa, flags);
 
 	if (ret)
 		return ERR_PTR(ret);

arch/arm64/kvm/vgic/vgic.c

@@ -29,9 +29,8 @@ struct vgic_global kvm_vgic_global_state __ro_after_init = {
  *       its->cmd_lock (mutex)
  *         its->its_lock (mutex)
  *           vgic_cpu->ap_list_lock		must be taken with IRQs disabled
- *             kvm->lpi_list_lock		must be taken with IRQs disabled
- *               vgic_dist->lpi_xa.xa_lock	must be taken with IRQs disabled
- *                 vgic_irq->irq_lock		must be taken with IRQs disabled
+ *             vgic_dist->lpi_xa.xa_lock	must be taken with IRQs disabled
+ *               vgic_irq->irq_lock		must be taken with IRQs disabled
  *
  * As the ap_list_lock might be taken from the timer interrupt handler,
  * we have to disable IRQs before taking this lock and everything lower

include/kvm/arm_vgic.h

@@ -280,9 +280,6 @@ struct vgic_dist {
 	 */
 	u64			propbaser;
 
-	/* Protects the lpi_list. */
-	raw_spinlock_t		lpi_list_lock;
-
 #define LPI_XA_MARK_DEBUG_ITER	XA_MARK_0
 	struct xarray		lpi_xa;