Merge branch kvm-arm64/mmio-rcu into kvmarm-master/next

* kvm-arm64/mmio-rcu:
  : .
  : Speed up MMIO registration by avoiding unnecessary RCU synchronisation,
  : courtesy of Keir Fraser (20250909100007.3136249-1-keirf@google.com).
  : .
  KVM: Avoid synchronize_srcu() in kvm_io_bus_register_dev()
  KVM: Implement barriers before accessing kvm->buses[] on SRCU read paths
  KVM: arm64: vgic: Explicitly implement vgic_dist::ready ordering
  KVM: arm64: vgic-init: Remove vgic_ready() macro

Signed-off-by: Marc Zyngier <maz@kernel.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 15656b7fba6c..103be35caf0d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -206,6 +206,7 @@ struct kvm_io_range {
 struct kvm_io_bus {
 	int dev_count;
 	int ioeventfd_count;
+	struct rcu_head rcu;
 	struct kvm_io_range range[];
 };
 
@@ -966,11 +967,15 @@ static inline bool kvm_dirty_log_manual_protect_and_init_set(struct kvm *kvm)
 	return !!(kvm->manual_dirty_log_protect & KVM_DIRTY_LOG_INITIALLY_SET);
 }
 
+/*
+ * Get a bus reference under the update-side lock. No long-term SRCU reader
+ * references are permitted, to avoid stale reads vs concurrent IO
+ * registrations.
+ */
 static inline struct kvm_io_bus *kvm_get_bus(struct kvm *kvm, enum kvm_bus idx)
 {
-	return srcu_dereference_check(kvm->buses[idx], &kvm->srcu,
-				      lockdep_is_held(&kvm->slots_lock) ||
-				      !refcount_read(&kvm->users_count));
+	return rcu_dereference_protected(kvm->buses[idx],
+					 lockdep_is_held(&kvm->slots_lock));
 }
 
 static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i)