linux-kernel - [PATCH v4 10/10] KVM: arm64: vgic: Don't acquire the lpi_list_lock in vgic_put

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Date: Wed, 21 Feb 2024 05:42:53 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: kvmarm@...ts.linux.dev
Cc: kvm@...r.kernel.org,
	Marc Zyngier <maz@...nel.org>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-kernel@...r.kernel.org,
	Eric Auger <eric.auger@...hat.com>,
	Oliver Upton <oliver.upton@...ux.dev>
Subject: [PATCH v4 10/10] KVM: arm64: vgic: Don't acquire the lpi_list_lock in vgic_put_irq()

The LPI xarray's xa_lock is sufficient for synchronizing writers when
freeing a given LPI. Furthermore, readers can only take a new reference
on an IRQ if it was already nonzero.

Stop taking the lpi_list_lock unnecessarily and get rid of
__vgic_put_lpi_locked().

Signed-off-by: Oliver Upton <oliver.upton@...ux.dev>
---
 arch/arm64/kvm/vgic/vgic-its.c |  4 ++--
 arch/arm64/kvm/vgic/vgic.c     | 28 +++++++++-------------------
 arch/arm64/kvm/vgic/vgic.h     |  1 -
 3 files changed, 11 insertions(+), 22 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index dad6f0ee7c49..f6025886071c 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -649,7 +649,7 @@ static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
 	 * was in the cache, and increment it on the new interrupt.
 	 */
 	if (cte->irq)
-		__vgic_put_lpi_locked(kvm, cte->irq);
+		vgic_put_irq(kvm, cte->irq);
 
 	/*
 	 * The irq refcount is guaranteed to be nonzero while holding the
@@ -686,7 +686,7 @@ void vgic_its_invalidate_cache(struct kvm *kvm)
 		if (!cte->irq)
 			break;
 
-		__vgic_put_lpi_locked(kvm, cte->irq);
+		vgic_put_irq(kvm, cte->irq);
 		cte->irq = NULL;
 	}
 
diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index df9e1aa1956c..f963f410788a 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -111,22 +111,6 @@ static void vgic_irq_release(struct kref *ref)
 {
 }
 
-/*
- * Drop the refcount on the LPI. Must be called with lpi_list_lock held.
- */
-void __vgic_put_lpi_locked(struct kvm *kvm, struct vgic_irq *irq)
-{
-	struct vgic_dist *dist = &kvm->arch.vgic;
-
-	if (!kref_put(&irq->refcount, vgic_irq_release))
-		return;
-
-	xa_erase(&dist->lpi_xa, irq->intid);
-	atomic_dec(&dist->lpi_count);
-
-	kfree_rcu(irq, rcu);
-}
-
 void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
@@ -135,9 +119,15 @@ void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
 	if (irq->intid < VGIC_MIN_LPI)
 		return;
 
-	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
-	__vgic_put_lpi_locked(kvm, irq);
-	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
+	if (!kref_put(&irq->refcount, vgic_irq_release))
+		return;
+
+	xa_lock_irqsave(&dist->lpi_xa, flags);
+	__xa_erase(&dist->lpi_xa, irq->intid);
+	xa_unlock_irqrestore(&dist->lpi_xa, flags);
+
+	atomic_dec(&dist->lpi_count);
+	kfree_rcu(irq, rcu);
 }
 
 void vgic_flush_pending_lpis(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index f874b9932c5a..0c2b82de8fa3 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -180,7 +180,6 @@ vgic_get_mmio_region(struct kvm_vcpu *vcpu, struct vgic_io_device *iodev,
 		     gpa_t addr, int len);
 struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
 			      u32 intid);
-void __vgic_put_lpi_locked(struct kvm *kvm, struct vgic_irq *irq);
 void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq);
 bool vgic_get_phys_line_level(struct vgic_irq *irq);
 void vgic_irq_set_phys_pending(struct vgic_irq *irq, bool pending);
-- 
2.44.0.rc0.258.g7320e95886-goog