[PATCH 01/20] KVM: Treat the device list as an rculist

[Oliver Upton <oliver.upton@linux.dev>]

A subsequent change to KVM/arm64 will necessitate walking the device
list outside of the kvm->lock. Prepare by converting to an rculist.
Note that this has zero effect the destruction path, as every reader
should be protected by a valid reference on the KVM struct.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 virt/kvm/kvm_main.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c681149c382a..a1423f8064b0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1326,10 +1326,12 @@ static void kvm_destroy_devices(struct kvm *kvm)
 	/*
 	 * We do not need to take the kvm->lock here, because nobody else
 	 * has a reference to the struct kvm at this point and therefore
-	 * cannot access the devices list anyhow.
+	 * cannot access the devices list anyhow. Furthermore, there are no RCU
+	 * readers after the last reference is dropped, so there is no need to
+	 * defer destruction until a grace period has elapsed.
 	 */
 	list_for_each_entry_safe(dev, tmp, &kvm->devices, vm_node) {
-		list_del(&dev->vm_node);
+		list_del_rcu(&dev->vm_node);
 		dev->ops->destroy(dev);
 	}
 }
@@ -4781,7 +4783,7 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
 		kfree(dev);
 		return ret;
 	}
-	list_add(&dev->vm_node, &kvm->devices);
+	list_add_rcu(&dev->vm_node, &kvm->devices);
 	mutex_unlock(&kvm->lock);
 
 	if (ops->init)
-- 
2.44.0.rc1.240.g4c46232300-goog