linux-kernel - Re: [PATCH v2] virtio_net: Fix mismatched buf address when unmapping for small packets

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Message-ID: <CACGkMEsMnEX25+-jyn3sjwF4iDEFCWKX2478dK-mf-fJeBrKtA@mail.gmail.com>
Date: Wed, 4 Sep 2024 14:31:42 +0800
From: Jason Wang <jasowang@...hat.com>
To: Wenbo Li <liwenbo.martin@...edance.com>
Cc: mst@...hat.com, xuanzhuo@...ux.alibaba.com, eperezma@...hat.com, 
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Jiahui Cen <cenjiahui@...edance.com>, 
	Ying Fang <fangying.tommy@...edance.com>
Subject: Re: [PATCH v2] virtio_net: Fix mismatched buf address when unmapping
 for small packets

On Wed, Sep 4, 2024 at 2:10 PM Wenbo Li <liwenbo.martin@...edance.com> 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.
>
> 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@...edance.com>
> Signed-off-by: Jiahui Cen <cenjiahui@...edance.com>
> Signed-off-by: Ying Fang <fangying.tommy@...edance.com>
> ---
>  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)

header_offset is unused?

> +{
> +       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
>

Thanks