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References: <20240115194840.1183077-1-andrew@daynix.com>
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From: Yuri Benditovich <yuri.benditovich@daynix.com>
Date: Mon, 15 Jan 2024 23:44:32 +0200
Message-ID: <CAOEp5Ofk5NrKujDApLXT6RL=hD6b4NFxv9GZ-NSvkbJvRYtG8Q@mail.gmail.com>
Subject: Re: [PATCH 1/1] vhost: Added pad cleanup if vnet_hdr is not present.
To: linux-kernel@vger.kernel.org
Cc: mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org, 
	virtualization@lists.linux.dev, netdev@vger.kernel.org, yan@daynix.com, 
	Andrew Melnychenko <andrew@daynix.com>
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See also https://issues.redhat.com/browse/RHEL-1303


On Mon, Jan 15, 2024 at 9:48=E2=80=AFPM Andrew Melnychenko <andrew@daynix.c=
om> wrote:
>
> When the Qemu launched with vhost but without tap vnet_hdr,
> vhost tries to copy vnet_hdr from socket iter with size 0
> to the page that may contain some trash.
> That trash can be interpreted as unpredictable values for
> vnet_hdr.
> That leads to dropping some packets and in some cases to
> stalling vhost routine when the vhost_net tries to process
> packets and fails in a loop.
>
> Qemu options:
>   -netdev tap,vhost=3Don,vnet_hdr=3Doff,...
>
> Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
> ---
>  drivers/vhost/net.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index f2ed7167c848..57411ac2d08b 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -735,6 +735,9 @@ static int vhost_net_build_xdp(struct vhost_net_virtq=
ueue *nvq,
>         hdr =3D buf;
>         gso =3D &hdr->gso;
>
> +       if (!sock_hlen)
> +               memset(buf, 0, pad);
> +
>         if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
>             vhost16_to_cpu(vq, gso->csum_start) +
>             vhost16_to_cpu(vq, gso->csum_offset) + 2 >
> --
> 2.43.0
>