[PATCH 06/15] KVM: arm64: vgic: Use atomics to count LPIs

Oliver Upton
2024-01-24T20:49:34Z

Switch to using atomics for LPI accounting, allowing vgic_irq references
to be dropped in parallel.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
arch/arm64/kvm/vgic/vgic-debug.c | 2 +-
arch/arm64/kvm/vgic/vgic-its.c | 4 ++--
arch/arm64/kvm/vgic/vgic.c | 2 +-
include/kvm/arm_vgic.h | 4 ++--
4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-debug.c b/arch/arm64/kvm/vgic/vgic-debug.c
index 85606a531dc3..389025ce7749 100644
--- a/arch/arm64/kvm/vgic/vgic-debug.c
+++ b/arch/arm64/kvm/vgic/vgic-debug.c
@@ -149,7 +149,7 @@ 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", dist->lpi_list_count);
+ seq_printf(s, "nr_lpis:\t%d\n", atomic_read(&dist->lpi_count));
seq_printf(s, "enabled:\t%d\n", dist->enabled);
seq_printf(s, "\n");

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index 0486d3779d11..1d912a595b71 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -97,7 +97,7 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
return ERR_PTR(ret);
}

- dist->lpi_list_count++;
+ atomic_inc(&dist->lpi_count);

out_unlock:
raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
@@ -342,7 +342,7 @@ int vgic_copy_lpi_list(struct kvm *kvm, struct kvm_vcpu *vcpu, u32 **intid_ptr)
* command). If coming from another path (such as enabling LPIs),
* we must be careful not to overrun the array.
*/
- irq_count = READ_ONCE(dist->lpi_list_count);
+ irq_count = atomic_read(&dist->lpi_count);
intids = kmalloc_array(irq_count, sizeof(intids[0]), GFP_KERNEL_ACCOUNT);
if (!intids)
return -ENOMEM;
diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index e58ce68e325c..5988d162b765 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -122,7 +122,7 @@ void __vgic_put_lpi_locked(struct kvm *kvm, struct vgic_irq *irq)
return;

xa_erase(&dist->lpi_xa, irq->intid);
- dist->lpi_list_count--;
+ atomic_dec(&dist->lpi_count);

kfree(irq);
}
diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index 39037db3fa90..e944536feee8 100644
--- a/include/kvm/arm_vgic.h
+++ b/include/kvm/arm_vgic.h
@@ -274,10 +274,10 @@ struct vgic_dist {
*/
u64 propbaser;

- /* Protects the lpi_list and the count value below. */
+ /* Protects the lpi_list. */
raw_spinlock_t lpi_list_lock;
struct xarray lpi_xa;
- int lpi_list_count;
+ atomic_t lpi_count;

/* LPI translation cache */
struct list_head lpi_translation_cache;
--
2.43.0.429.g432eaa2c6b-goog