[PATCH v2 09/23] KVM: arm64: vgic: Rely on RCU protection in vgic_get_lpi()
From: Oliver Upton
Date: Tue Feb 13 2024 - 04:36:35 EST
Stop acquiring the lpi_list_lock in favor of RCU for protecting
the read-side critical section in vgic_get_lpi(). In order for this to
be safe, we also need to be careful not to take a reference on an irq
with a refcount of 0, as it is about to be freed.
Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx>
---
arch/arm64/kvm/vgic/vgic.c | 9 ++++-----
arch/arm64/kvm/vgic/vgic.h | 14 +++++++++++---
2 files changed, 15 insertions(+), 8 deletions(-)
diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index be3ed4c5e1fa..128ae53a0a55 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -62,15 +62,14 @@ static struct vgic_irq *vgic_get_lpi(struct kvm *kvm, u32 intid)
{
struct vgic_dist *dist = &kvm->arch.vgic;
struct vgic_irq *irq = NULL;
- unsigned long flags;
- raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
+ rcu_read_lock();
irq = xa_load(&dist->lpi_xa, intid);
- if (irq)
- vgic_get_irq_kref(irq);
+ if (!vgic_try_get_irq_kref(irq))
+ irq = NULL;
- raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
+ rcu_read_unlock();
return irq;
}
diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index 8d134569d0a1..f874b9932c5a 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -220,12 +220,20 @@ void vgic_v2_vmcr_sync(struct kvm_vcpu *vcpu);
void vgic_v2_save_state(struct kvm_vcpu *vcpu);
void vgic_v2_restore_state(struct kvm_vcpu *vcpu);
-static inline void vgic_get_irq_kref(struct vgic_irq *irq)
+static inline bool vgic_try_get_irq_kref(struct vgic_irq *irq)
{
+ if (!irq)
+ return false;
+
if (irq->intid < VGIC_MIN_LPI)
- return;
+ return true;
- kref_get(&irq->refcount);
+ return kref_get_unless_zero(&irq->refcount);
+}
+
+static inline void vgic_get_irq_kref(struct vgic_irq *irq)
+{
+ WARN_ON_ONCE(!vgic_try_get_irq_kref(irq));
}
void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu);
--
2.43.0.687.g38aa6559b0-goog