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From:   Arseniy Krasnov <AVKrasnov@sberdevices.ru>
To:     Stefan Hajnoczi <stefanha@redhat.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>
CC:     <kvm@vger.kernel.org>, <virtualization@lists.linux-foundation.org>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <kernel@sberdevices.ru>, <oxffffaa@gmail.com>,
        <avkrasnov@sberdevices.ru>,
        Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Subject: [RFC PATCH v2 03/15] vsock/virtio: non-linear skb handling support
Date:   Sun, 23 Apr 2023 22:26:31 +0300
Message-ID: <20230423192643.1537470-4-AVKrasnov@sberdevices.ru>
In-Reply-To: <20230423192643.1537470-1-AVKrasnov@sberdevices.ru>
References: <20230423192643.1537470-1-AVKrasnov@sberdevices.ru>
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Precedence: bulk

Use pages of non-linear skb as buffers in virtio tx queue.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
---
 net/vmw_vsock/virtio_transport.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index e95df847176b..1c269c3f010d 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -100,7 +100,9 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 	vq = vsock->vqs[VSOCK_VQ_TX];
 
 	for (;;) {
-		struct scatterlist hdr, buf, *sgs[2];
+		/* +1 is for packet header. */
+		struct scatterlist *sgs[MAX_SKB_FRAGS + 1];
+		struct scatterlist bufs[MAX_SKB_FRAGS + 1];
 		int ret, in_sg = 0, out_sg = 0;
 		struct sk_buff *skb;
 		bool reply;
@@ -111,12 +113,30 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 
 		virtio_transport_deliver_tap_pkt(skb);
 		reply = virtio_vsock_skb_reply(skb);
+		sg_init_one(&bufs[0], virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
+		sgs[out_sg++] = &bufs[0];
+
+		if (skb_is_nonlinear(skb)) {
+			int i;
+
+			for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+				struct page *data_page = skb_shinfo(skb)->frags[i].bv_page;
+
+				/* We will use 'page_to_virt()' for userspace page here,
+				 * because virtio layer will call 'virt_to_phys()' later
+				 * to fill buffer descriptor. We don't touch memory at
+				 * "virtual" address of this page.
+				 */
+				sg_init_one(&bufs[i + 1],
+					    page_to_virt(data_page), PAGE_SIZE);
+				sgs[out_sg++] = &bufs[i + 1];
+			}
+		} else {
+			if (skb->len > 0) {
+				sg_init_one(&bufs[1], skb->data, skb->len);
+				sgs[out_sg++] = &bufs[1];
+			}
 
-		sg_init_one(&hdr, virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
-		sgs[out_sg++] = &hdr;
-		if (skb->len > 0) {
-			sg_init_one(&buf, skb->data, skb->len);
-			sgs[out_sg++] = &buf;
 		}
 
 		ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
-- 
2.25.1