Re: [External] Re: [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets
From: Wenbo Li
Date: Wed Sep 04 2024 - 03:53:14 EST
Thank you. I'll fix these in v3.
On 9/4/24 15:30, Xuan Zhuo wrote:
On Wed, 4 Sep 2024 15:21:28 +0800, =?utf-8?b?5paH5Y2a5p2O?= <liwenbo.martin@xxxxxxxxxxxxx> wrote:
When SWIOTLB is enabled, a DMA map will allocate a bounce buffer for real
DMA operations,
and when unmapping, SWIOTLB copies the content in the bounce buffer to the
driver-allocated
buffer (the `buf` variable). Such copy only synchronizes data in the buffer
range, not the whole page.
So we should give the correct offset for DMA unmapping.
I see.
But I think we should pass the "correct" buf to virtio core as the "data" by
virtqueue_add_inbuf_ctx().
In the merge mode, we pass the pointer that points to the virtnet header.
In the small mode, we pass the pointer that points to the virtnet header - offset.
But this is not the only problem, we try to get the virtnet header by the buf
inside receive_buf(before receive_small).
flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
So I think it is time to unify the buf that passed to the virtio core into a
pointer pointed to the virtnet header.
Thanks.
Thanks.
On Wed, Sep 4, 2024 at 2:46 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
On Wed, 4 Sep 2024 14:10:09 +0800, Wenbo Li <liwenbo.martin@xxxxxxxxxxxxx>
wrote:
Currently, the virtio-net driver will perform a pre-dma-mapping for
small or mergeable RX buffer. But for small packets, a mismatched
address
without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.
Will used virt_to_head_page(), so could you say more about it?
struct page *page = virt_to_head_page(buf);
Thanks.
That will result in unsynchronized buffers when SWIOTLB is enabled, for
example, when running as a TDX guest.
This patch handles small and mergeable packets separately and fixes
the mismatched buffer address.
Changes from v1: Use ctx to get xdp_headroom.
Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling
mergeable buffers")
Signed-off-by: Wenbo Li <liwenbo.martin@xxxxxxxxxxxxx>
Signed-off-by: Jiahui Cen <cenjiahui@xxxxxxxxxxxxx>
Signed-off-by: Ying Fang <fangying.tommy@xxxxxxxxxxxxx>
---
drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c6af18948..cbc3c0ae4 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -891,6 +891,23 @@ static void *virtnet_rq_get_buf(struct
receive_queue *rq, u32 *len, void **ctx)
return buf;
}
+static void *virtnet_rq_get_buf_small(struct receive_queue *rq,
+ u32 *len,
+ void **ctx,
+ unsigned int header_offset)
+{
+ void *buf;
+ unsigned int xdp_headroom;
+
+ buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
+ if (buf) {
+ xdp_headroom = (unsigned long)*ctx;
+ virtnet_rq_unmap(rq, buf + VIRTNET_RX_PAD + xdp_headroom,
*len);
+ }
+
+ return buf;
+}
+
static void virtnet_rq_init_one_sg(struct receive_queue *rq, void
*buf, u32 len)
{
struct virtnet_rq_dma *dma;
@@ -2692,13 +2709,23 @@ static int virtnet_receive_packets(struct
virtnet_info *vi,
int packets = 0;
void *buf;
- if (!vi->big_packets || vi->mergeable_rx_bufs) {
+ if (vi->mergeable_rx_bufs) {
void *ctx;
while (packets < budget &&
(buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
receive_buf(vi, rq, buf, len, ctx, xdp_xmit,
stats);
packets++;
}
+ } else if (!vi->big_packets) {
+ void *ctx;
+ unsigned int xdp_headroom = virtnet_get_headroom(vi);
+ unsigned int header_offset = VIRTNET_RX_PAD +
xdp_headroom;
+
+ while (packets < budget &&
+ (buf = virtnet_rq_get_buf_small(rq, &len, &ctx,
header_offset))) {
+ receive_buf(vi, rq, buf, len, ctx, xdp_xmit,
stats);
+ packets++;
+ }
} else {
while (packets < budget &&
(buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
--
2.20.1