netdev - [PATCH net-next 2/2] virtio-net: fix the XDP truesize calculation for mergeable buffers

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Date:   Wed,  6 May 2020 14:16:33 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     mst@...hat.com, jasowang@...hat.com
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: [PATCH net-next 2/2] virtio-net: fix the XDP truesize calculation for mergeable buffers

We should not exclude headroom and tailroom when XDP is set. So this
patch fixes this by initializing the truesize from PAGE_SIZE when XDP
is set.

Cc: Jesper Dangaard Brouer <brouer@...hat.com>
Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/virtio_net.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 98dd75b665a5..3f3aa8308918 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1184,7 +1184,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
 	char *buf;
 	void *ctx;
 	int err;
-	unsigned int len, hole;
+	unsigned int len, hole, truesize;
 
 	/* Extra tailroom is needed to satisfy XDP's assumption. This
 	 * means rx frags coalescing won't work, but consider we've
@@ -1194,6 +1194,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
 	if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
 		return -ENOMEM;
 
+	truesize = headroom ? PAGE_SIZE : len;
 	buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
 	buf += headroom; /* advance address leaving hole at front of pkt */
 	get_page(alloc_frag->page);
@@ -1205,11 +1206,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
 		 * the current buffer.
 		 */
 		len += hole;
+		truesize += hole;
 		alloc_frag->offset += hole;
 	}
 
 	sg_init_one(rq->sg, buf, len);
-	ctx = mergeable_len_to_ctx(len, headroom);
+	ctx = mergeable_len_to_ctx(truesize, headroom);
 	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
 	if (err < 0)
 		put_page(virt_to_head_page(buf));
-- 
2.20.1