[PATCH v1 2/3] KVM: arm64: Reimplement vgic-debug XArray iteration
Fuad Tabba
tabba at google.com
Mon Feb 2 00:57:20 PST 2026
The vgic-debug interface implementation uses XArray marks
(`LPI_XA_MARK_DEBUG_ITER`) to "snapshot" LPIs at the start of iteration.
This modifies global state for a read-only operation and complicates
reference counting, leading to leaks if iteration is aborted or fails.
Reimplement the iterator to use dynamic iteration logic:
- Remove `lpi_idx` from `struct vgic_state_iter`.
- Replace the XArray marking mechanism with dynamic iteration using
`xa_find_after(..., XA_PRESENT)`.
- Wrap XArray traversals in `rcu_read_lock()`/`rcu_read_unlock()` to
ensure safety against concurrent modifications (e.g., LPI unmapping).
- Handle potential races where an LPI is removed during iteration by
gracefully skipping it in `show()`, rather than warning.
- Remove the unused `LPI_XA_MARK_DEBUG_ITER` definition.
This simplifies the lifecycle management of the iterator and prevents
resource leaks associated with the marking mechanism, and paves the way
for using a standard seq_file iterator.
Signed-off-by: Fuad Tabba <tabba at google.com>
---
arch/arm64/kvm/vgic/vgic-debug.c | 68 ++++++++++----------------------
include/kvm/arm_vgic.h | 1 -
2 files changed, 20 insertions(+), 49 deletions(-)
diff --git a/arch/arm64/kvm/vgic/vgic-debug.c b/arch/arm64/kvm/vgic/vgic-debug.c
index bb92853d1fd3..ec3d0c1fe703 100644
--- a/arch/arm64/kvm/vgic/vgic-debug.c
+++ b/arch/arm64/kvm/vgic/vgic-debug.c
@@ -25,11 +25,9 @@
struct vgic_state_iter {
int nr_cpus;
int nr_spis;
- int nr_lpis;
int dist_id;
int vcpu_id;
unsigned long intid;
- int lpi_idx;
};
static void iter_next(struct kvm *kvm, struct vgic_state_iter *iter)
@@ -45,13 +43,15 @@ static void iter_next(struct kvm *kvm, struct vgic_state_iter *iter)
* 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) &&
- iter->nr_lpis) {
- 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++;
+ if (iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS - 1)) {
+ if (iter->intid == VGIC_LPI_MAX_INTID + 1)
+ return;
+
+ rcu_read_lock();
+ if (!xa_find_after(&dist->lpi_xa, &iter->intid,
+ VGIC_LPI_MAX_INTID, XA_PRESENT))
+ iter->intid = VGIC_LPI_MAX_INTID + 1;
+ rcu_read_unlock();
return;
}
@@ -61,44 +61,21 @@ static void iter_next(struct kvm *kvm, struct vgic_state_iter *iter)
iter->intid = 0;
}
-static int iter_mark_lpis(struct kvm *kvm)
+static int vgic_count_lpis(struct kvm *kvm)
{
struct vgic_dist *dist = &kvm->arch.vgic;
- unsigned long intid, flags;
struct vgic_irq *irq;
+ unsigned long intid;
int nr_lpis = 0;
- xa_lock_irqsave(&dist->lpi_xa, flags);
-
- xa_for_each(&dist->lpi_xa, intid, irq) {
- if (!vgic_try_get_irq_ref(irq))
- continue;
-
- __xa_set_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);
+ rcu_read_lock();
+ xa_for_each(&dist->lpi_xa, intid, irq)
nr_lpis++;
- }
-
- xa_unlock_irqrestore(&dist->lpi_xa, flags);
+ rcu_read_unlock();
return nr_lpis;
}
-static void iter_unmark_lpis(struct kvm *kvm)
-{
- struct vgic_dist *dist = &kvm->arch.vgic;
- unsigned long intid, flags;
- struct vgic_irq *irq;
-
- xa_for_each_marked(&dist->lpi_xa, intid, irq, LPI_XA_MARK_DEBUG_ITER) {
- xa_lock_irqsave(&dist->lpi_xa, flags);
- __xa_clear_mark(&dist->lpi_xa, intid, LPI_XA_MARK_DEBUG_ITER);
- xa_unlock_irqrestore(&dist->lpi_xa, flags);
-
- /* vgic_put_irq() expects to be called outside of the xa_lock */
- vgic_put_irq(kvm, irq);
- }
-}
-
static void iter_init(struct kvm *kvm, struct vgic_state_iter *iter,
loff_t pos)
{
@@ -108,8 +85,6 @@ 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 = iter_mark_lpis(kvm);
/* Fast forward to the right position if needed */
while (pos--)
@@ -121,7 +96,7 @@ static bool end_of_vgic(struct vgic_state_iter *iter)
return iter->dist_id > 0 &&
iter->vcpu_id == iter->nr_cpus &&
iter->intid >= (iter->nr_spis + VGIC_NR_PRIVATE_IRQS) &&
- (!iter->nr_lpis || iter->lpi_idx > iter->nr_lpis);
+ iter->intid > VGIC_LPI_MAX_INTID;
}
static void *vgic_debug_start(struct seq_file *s, loff_t *pos)
@@ -178,7 +153,6 @@ static void vgic_debug_stop(struct seq_file *s, void *v)
mutex_lock(&kvm->arch.config_lock);
iter = kvm->arch.vgic.iter;
- iter_unmark_lpis(kvm);
kfree(iter);
kvm->arch.vgic.iter = NULL;
mutex_unlock(&kvm->arch.config_lock);
@@ -188,13 +162,14 @@ 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;
+ struct kvm *kvm = s->private;
seq_printf(s, "Distributor\n");
seq_printf(s, "===========\n");
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", iter->nr_lpis);
+ seq_printf(s, "nr_lpis:\t%d\n", vgic_count_lpis(kvm));
seq_printf(s, "enabled:\t%d\n", dist->enabled);
seq_printf(s, "\n");
@@ -291,16 +266,13 @@ 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.
- */
if (iter->intid < VGIC_NR_PRIVATE_IRQS)
irq = vgic_get_vcpu_irq(vcpu, iter->intid);
else
irq = vgic_get_irq(kvm, iter->intid);
- if (WARN_ON_ONCE(!irq))
- return -EINVAL;
+
+ if (!irq)
+ return 0;
raw_spin_lock_irqsave(&irq->irq_lock, flags);
print_irq_state(s, irq, vcpu);
diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index b261fb3968d0..d32fafbd2907 100644
--- a/include/kvm/arm_vgic.h
+++ b/include/kvm/arm_vgic.h
@@ -300,7 +300,6 @@ struct vgic_dist {
*/
u64 propbaser;
-#define LPI_XA_MARK_DEBUG_ITER XA_MARK_0
struct xarray lpi_xa;
/* used by vgic-debug */
--
2.53.0.rc1.225.gd81095ad13-goog
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