linux-kernel - [PATCH V3 3/9] virtio: introduce config op to synchronize vring callbacks

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Date:   Mon, 25 Apr 2022 10:44:12 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     jasowang@...hat.com, mst@...hat.com, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Cc:     sgarzare@...hat.com, eperezma@...hat.com, lulu@...hat.com,
        tglx@...utronix.de, peterz@...radead.org, paulmck@...nel.org,
        maz@...nel.org, pasic@...ux.ibm.com, cohuck@...hat.com
Subject: [PATCH V3 3/9] virtio: introduce config op to synchronize vring callbacks

This patch introduces new virtio config op to vring
callbacks. Transport specific method is required to make sure the
write before this function is visible to the vring_interrupt() that is
called after the return of this function. For the transport that
doesn't provide synchronize_vqs(), use synchornize_rcu() which
synchronize with IRQ implicitly as a fallback.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>
Cc: Halil Pasic <pasic@...ux.ibm.com>
Cc: Cornelia Huck <cohuck@...hat.com>
Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 include/linux/virtio_config.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index b341dd62aa4d..14fe89ff99c7 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -57,6 +57,10 @@ struct virtio_shm_region {
  *		include a NULL entry for vqs unused by driver
  *	Returns 0 on success or error status
  * @del_vqs: free virtqueues found by find_vqs().
+ * @synchronize_cbs: synchronize with the virtqueue callbacks (optional)
+ *      Make sure the writes commited before this method is visible to
+ *      vring_interrupt() which is called after this method.
+ *      vdev: the virtio_device
  * @get_features: get the array of feature bits for this device.
  *	vdev: the virtio_device
  *	Returns the first 64 feature bits (all we currently need).
@@ -89,6 +93,7 @@ struct virtio_config_ops {
 			const char * const names[], const bool *ctx,
 			struct irq_affinity *desc);
 	void (*del_vqs)(struct virtio_device *);
+	void (*synchronize_cbs)(struct virtio_device *);
 	u64 (*get_features)(struct virtio_device *vdev);
 	int (*finalize_features)(struct virtio_device *vdev);
 	const char *(*bus_name)(struct virtio_device *vdev);
@@ -217,6 +222,25 @@ int virtio_find_vqs_ctx(struct virtio_device *vdev, unsigned nvqs,
 				      desc);
 }
 
+/**
+ * virtio_synchronize_cbs - synchronize with virtqueue callbacks
+ * @vdev: the device
+ */
+static inline
+void virtio_synchronize_cbs(struct virtio_device *dev)
+{
+	if (dev->config->synchronize_cbs) {
+		dev->config->synchronize_cbs(dev);
+	} else {
+		/*
+		 * A best effort fallback to synchronize with
+		 * interrupts, preemption and softirq. See comment
+		 * above synchronize_rcu().
+		 */
+		synchronize_rcu();
+	}
+}
+
 /**
  * virtio_device_ready - enable vq use in probe function
  * @vdev: the device
-- 
2.25.1