linux-kernel - [RFC PATCH 14/16] virtio_ring: packed: introduce vring_reuse_bufs

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Message-Id: <20220424024044.94749-15-xuanzhuo@linux.alibaba.com>
Date:   Sun, 24 Apr 2022 10:40:42 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: [RFC PATCH 14/16] virtio_ring: packed: introduce vring_reuse_bufs_packed()

vring_reuse_bufs_packed() checks vring.desc forward based on
last_used_idx. The resulting buffers are the order in which they were
committed.

It is beneficial to ensure the order of buffers in the process of reuse.
For example, under virtio-net, if the order is not guaranteed, it may
lead to out-of-order tcp streams.

Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 45 ++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 8ca9985ffb4b..66f71e22ece0 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2041,6 +2041,51 @@ static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
 	return true;
 }
 
+static void vring_reuse_bufs_packed(struct vring_virtqueue *vq,
+				    struct vring_virtqueue_packed *vring,
+				    void (*recycle)(struct virtqueue *vq, void *buf))
+{
+	struct vring_desc_state_packed *state;
+	u32 last_used, id, desc_num = 0;
+	int err = 0;
+	void *buf;
+
+	last_used = vring->last_used_idx;
+
+	do {
+		id = le16_to_cpu(vring->vring.desc[last_used].id);
+
+		state = &vring->desc_state[id];
+
+		if (!state->data) {
+			last_used++;
+			goto next;
+		}
+
+		/* once add to vq fail, no more try add to vq. */
+		if (err >= 0) {
+			err = vring_copy_to_vq_packed(vq, vring, id);
+			if (err >= 0)
+				goto ok;
+		}
+
+		buf = state->data;
+		detach_buf_from_vring_packed(vring, vq, id, 0, NULL);
+		recycle(&vq->vq, buf);
+
+ok:
+		last_used += state->num;
+		desc_num += state->num;
+
+next:
+		if (unlikely(last_used >= vring->vring.num))
+			last_used -= vring->vring.num;
+
+	} while (last_used != vring->last_used_idx);
+
+	WARN_ON(vring->num_left != desc_num);
+}
+
 static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-- 
2.31.0