KVM: arm64: vgic-debug: Use an xarray mark for debug iterator

The vgic debug iterator is the final user of vgic_copy_lpi_list(), but
is a bit more complicated to transition to something else. Use a mark
in the LPI xarray to record the indices 'known' to the debug iterator.
Protect against the LPIs from being freed by associating an additional
reference with the xarray mark.

Rework iter_next() to let the xarray walk 'drive' the iteration after
visiting all of the SGIs, PPIs, and SPIs.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240422200158.2606761-6-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>

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

@@ -28,27 +28,65 @@ struct vgic_state_iter {
 	int nr_lpis;
 	int dist_id;
 	int vcpu_id;
-	int intid;
+	unsigned long intid;
 	int lpi_idx;
-	u32 *lpi_array;
 };
 
-static void iter_next(struct vgic_state_iter *iter)
+static void iter_next(struct kvm *kvm, struct vgic_state_iter *iter)
 {
+	struct vgic_dist *dist = &kvm->arch.vgic;
+
 	if (iter->dist_id == 0) {
 		iter->dist_id++;
 		return;
 	}
 
+	/*
+	 * Let the xarray drive the iterator after the last SPI, as the iterator
+	 * has exhausted the sequentially-allocated INTID space.
+	 */
+	if (iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS - 1)) {
+		if (iter->lpi_idx < iter->nr_lpis)
+			xa_find_after(&dist->lpi_xa, &iter->intid,
+				      VGIC_LPI_MAX_INTID,
+				      LPI_XA_MARK_DEBUG_ITER);
+		iter->lpi_idx++;
+		return;
+	}
+
 	iter->intid++;
 	if (iter->intid == VGIC_NR_PRIVATE_IRQS &&
 	    ++iter->vcpu_id < iter->nr_cpus)
 		iter->intid = 0;
+}
 
-	if (iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS)) {
-		if (iter->lpi_idx < iter->nr_lpis)
-			iter->intid = iter->lpi_array[iter->lpi_idx];
-		iter->lpi_idx++;
+static int iter_mark_lpis(struct kvm *kvm)
+{
+	struct vgic_dist *dist = &kvm->arch.vgic;
+	struct vgic_irq *irq;
+	unsigned long intid;
+	int nr_lpis = 0;
+
+	xa_for_each(&dist->lpi_xa, intid, irq) {
+		if (!vgic_try_get_irq_kref(irq))
+			continue;
+
+		xa_set_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);
+		nr_lpis++;
+	}
+
+	return nr_lpis;
+}
+
+static void iter_unmark_lpis(struct kvm *kvm)
+{
+	struct vgic_dist *dist = &kvm->arch.vgic;
+	struct vgic_irq *irq;
+	unsigned long intid;
+
+	xa_for_each(&dist->lpi_xa, intid, irq) {
+		xa_clear_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);
+		vgic_put_irq(kvm, irq);
 	}
 }
 
@@ -61,15 +99,12 @@ static void iter_init(struct kvm *kvm, struct vgic_state_iter *iter,
 
 	iter->nr_cpus = nr_cpus;
 	iter->nr_spis = kvm->arch.vgic.nr_spis;
-	if (kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
-		iter->nr_lpis = vgic_copy_lpi_list(kvm, NULL, &iter->lpi_array);
-		if (iter->nr_lpis < 0)
-			iter->nr_lpis = 0;
-	}
+	if (kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3)
+		iter->nr_lpis = iter_mark_lpis(kvm);
 
 	/* Fast forward to the right position if needed */
 	while (pos--)
-		iter_next(iter);
+		iter_next(kvm, iter);
 }
 
 static bool end_of_vgic(struct vgic_state_iter *iter)
@@ -114,7 +149,7 @@ static void *vgic_debug_next(struct seq_file *s, void *v, loff_t *pos)
 	struct vgic_state_iter *iter = kvm->arch.vgic.iter;
 
 	++*pos;
-	iter_next(iter);
+	iter_next(kvm, iter);
 	if (end_of_vgic(iter))
 		iter = NULL;
 	return iter;
@@ -134,13 +169,14 @@ static void vgic_debug_stop(struct seq_file *s, void *v)
 
 	mutex_lock(&kvm->arch.config_lock);
 	iter = kvm->arch.vgic.iter;
-	kfree(iter->lpi_array);
+	iter_unmark_lpis(kvm);
 	kfree(iter);
 	kvm->arch.vgic.iter = NULL;
 	mutex_unlock(&kvm->arch.config_lock);
 }
 
-static void print_dist_state(struct seq_file *s, struct vgic_dist *dist)
+static void print_dist_state(struct seq_file *s, struct vgic_dist *dist,
+			     struct vgic_state_iter *iter)
 {
 	bool v3 = dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3;
 
@@ -149,7 +185,7 @@ static void print_dist_state(struct seq_file *s, struct vgic_dist *dist)
 	seq_printf(s, "vgic_model:\t%s\n", v3 ? "GICv3" : "GICv2");
 	seq_printf(s, "nr_spis:\t%d\n", dist->nr_spis);
 	if (v3)
-		seq_printf(s, "nr_lpis:\t%d\n", atomic_read(&dist->lpi_count));
+		seq_printf(s, "nr_lpis:\t%d\n", iter->nr_lpis);
 	seq_printf(s, "enabled:\t%d\n", dist->enabled);
 	seq_printf(s, "\n");
 
@@ -236,7 +272,7 @@ static int vgic_debug_show(struct seq_file *s, void *v)
 	unsigned long flags;
 
 	if (iter->dist_id == 0) {
-		print_dist_state(s, &kvm->arch.vgic);
+		print_dist_state(s, &kvm->arch.vgic, iter);
 		return 0;
 	}
 
@@ -246,11 +282,13 @@ static int vgic_debug_show(struct seq_file *s, void *v)
 	if (iter->vcpu_id < iter->nr_cpus)
 		vcpu = kvm_get_vcpu(kvm, iter->vcpu_id);
 
+	/*
+	 * Expect this to succeed, as iter_mark_lpis() takes a reference on
+	 * every LPI to be visited.
+	 */
 	irq = vgic_get_irq(kvm, vcpu, iter->intid);
-	if (!irq) {
-		seq_printf(s, "       LPI %4d freed\n", iter->intid);
-		return 0;
-	}
+	if (WARN_ON_ONCE(!irq))
+		return -EINVAL;
 
 	raw_spin_lock_irqsave(&irq->irq_lock, flags);
 	print_irq_state(s, irq, vcpu);

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

@@ -316,8 +316,6 @@ static int update_lpi_config(struct kvm *kvm, struct vgic_irq *irq,
 	return 0;
 }
 
-#define GIC_LPI_MAX_INTID	((1 << INTERRUPT_ID_BITS_ITS) - 1)
-
 /*
  * Create a snapshot of the current LPIs targeting @vcpu, so that we can
  * enumerate those LPIs without holding any lock.
@@ -347,7 +345,7 @@ int vgic_copy_lpi_list(struct kvm *kvm, struct kvm_vcpu *vcpu, u32 **intid_ptr)
 	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
 	rcu_read_lock();
 
-	xas_for_each(&xas, irq, GIC_LPI_MAX_INTID) {
+	xas_for_each(&xas, irq, VGIC_LPI_MAX_INTID) {
 		if (i == irq_count)
 			break;
 		/* We don't need to "get" the IRQ, as we hold the list lock. */

arch/arm64/kvm/vgic/vgic.h

@@ -16,6 +16,7 @@
 
 #define INTERRUPT_ID_BITS_SPIS	10
 #define INTERRUPT_ID_BITS_ITS	16
+#define VGIC_LPI_MAX_INTID	((1 << INTERRUPT_ID_BITS_ITS) - 1)
 #define VGIC_PRI_BITS		5
 
 #define vgic_irq_is_sgi(intid) ((intid) < VGIC_NR_SGIS)

include/kvm/arm_vgic.h

@@ -276,6 +276,8 @@ struct vgic_dist {
 
 	/* Protects the lpi_list. */
 	raw_spinlock_t		lpi_list_lock;
+
+#define LPI_XA_MARK_DEBUG_ITER	XA_MARK_0
 	struct xarray		lpi_xa;
 	atomic_t		lpi_count;