When the frag just got a page, then may lead to regression on VM.
Specially if the sysctl net.core.high_order_alloc_disable value is 1,
then the frag always get a page when do refill.
Which could see reliable crashes or scp failure (scp a file 100M in size
to VM):
The issue is that the virtnet_rq_dma takes up 16 bytes at the beginning
of a new frag. When the frag size is larger than PAGE_SIZE,
everything is fine. However, if the frag is only one page and the
total size of the buffer and virtnet_rq_dma is larger than one page, an
overflow may occur.
Here, when the frag size is not enough, we reduce the buffer len to fix
this problem.
Fixes: f9dac92ba908 ("virtio_ring: enable premapped mode whatever use_dma_api")
Reported-by: "Si-Wei Liu" <si-wei.liu@xxxxxxxxxx>
Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
drivers/net/virtio_net.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index f8131f92a392..59a99bbaf852 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -926,9 +926,6 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
void *buf, *head;
dma_addr_t addr;
- if (unlikely(!skb_page_frag_refill(size, alloc_frag, gfp)))
- return NULL;
-
head = page_address(alloc_frag->page);
if (rq->do_dma) {
@@ -2423,6 +2420,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
len = SKB_DATA_ALIGN(len) +
SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+ if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
+ return -ENOMEM;
+
buf = virtnet_rq_alloc(rq, len, gfp);
if (unlikely(!buf))
return -ENOMEM;
@@ -2525,6 +2525,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
*/
len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
+ if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
+ return -ENOMEM;
+
+ if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
+ len -= sizeof(struct virtnet_rq_dma);
+
buf = virtnet_rq_alloc(rq, len + room, gfp);
if (unlikely(!buf))
return -ENOMEM;
--
2.32.0.3.g01195cf9f
