linux-kernel - Re: [PATCH net 2/4] virtio-net: remove redundant truesize check with PAGE

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Message-ID: <CACGkMEuZTP+xPCWuSGwiApWEj_PuOxb5yOeR3t-Bga1t+svawQ@mail.gmail.com>
Date: Thu, 26 Jun 2025 10:37:01 +0800
From: Jason Wang <jasowang@...hat.com>
To: Bui Quang Minh <minhquangbui99@...il.com>
Cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez <eperezma@...hat.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	Stanislav Fomichev <sdf@...ichev.me>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH net 2/4] virtio-net: remove redundant truesize check with PAGE_SIZE

On Thu, Jun 26, 2025 at 12:10 AM Bui Quang Minh
<minhquangbui99@...il.com> wrote:
>
> The truesize is guaranteed not to exceed PAGE_SIZE in
> get_mergeable_buf_len(). It is saved in mergeable context, which is not
> changeable by the host side,

This really depends on the security model.

> so the check in receive path is quite
> redundant.
>
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> ---
>  drivers/net/virtio_net.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 2a130a3e50ac..6f9fedad4a5e 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2144,9 +2144,9 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>  {
>         struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
>         unsigned int headroom, tailroom, room;
> -       unsigned int truesize, cur_frag_size;
>         struct skb_shared_info *shinfo;
>         unsigned int xdp_frags_truesz = 0;
> +       unsigned int truesize;
>         struct page *page;
>         skb_frag_t *frag;
>         int offset;
> @@ -2194,9 +2194,8 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>                 tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
>                 room = SKB_DATA_ALIGN(headroom + tailroom);
>
> -               cur_frag_size = truesize;
> -               xdp_frags_truesz += cur_frag_size;
> -               if (unlikely(len > truesize - room || cur_frag_size > PAGE_SIZE)) {
> +               xdp_frags_truesz += truesize;
> +               if (unlikely(len > truesize - room)) {
>                         put_page(page);
>                         pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
>                                  dev->name, len, (unsigned long)(truesize - room));
> --
> 2.43.0
>

Acked-by: Jason Wang <jasowang@...hat.com>

Thanks