Re: [dpdk-dev] [PATCH] net/virtio-user: fix cannot get initialized

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Fri, Apr 07, 2017 at 07:57:40AM +0000, Jianfeng Tan wrote:
> After the introduction of vhost MTU, VIRTIO_NET_F_MTU is enabled
> by default. However, virtio-user vtpci does not support to get
> MTU from device yet, i.e., vtpci_read_dev_config(MTU) fails.
> Plus, struct virtio_net_config is defined as a uninitialized
> variable, and could be different values in
> virtio_negotiate_features() and virtio_init_device().
> 
> In some cases, it passes the check in virtio_negotiate_features()
> but fails the check in virtio_init_device(). As a result,
> virtio-user canno be initialized.
> 
> To fix it, (1) accessing uninitialized variable is not a good
> practice, so initialize it as zero; (2) explicitly disable MTU
> feature in virtio-user.
> 
> Fixes: 49d26d9e3f47 ("net/virtio: support MTU feature")
> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
> Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> 
> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
>  drivers/net/virtio/virtio_ethdev.c               | 4 ++--
>  drivers/net/virtio/virtio_user/virtio_user_dev.c | 6 ++++++
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
> index 78cb3e8..4c43784 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -1163,7 +1163,7 @@ virtio_negotiate_features(struct virtio_hw *hw, uint64_t req_features)
>  
>  	/* If supported, ensure MTU value is valid before acknowledging it. */
>  	if (host_features & req_features & (1ULL << VIRTIO_NET_F_MTU)) {
> -		struct virtio_net_config config;
> +		struct virtio_net_config config = {0};

virtio-user does not support the MTU feature, this patch should not be
reached. The virtio-user feature negotiation should be broken.

	--yliu

>  
>  		vtpci_read_dev_config(hw,
>  			offsetof(struct virtio_net_config, mtu),
> @@ -1332,7 +1332,7 @@ virtio_init_device(struct rte_eth_dev *eth_dev, uint64_t req_features)
>  {
>  	struct virtio_hw *hw = eth_dev->data->dev_private;
>  	struct virtio_net_config *config;
> -	struct virtio_net_config local_config;
> +	struct virtio_net_config local_config = {0};
>  	struct rte_pci_device *pci_dev = NULL;
>  	int ret;
>  
> diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c b/drivers/net/virtio/virtio_user/virtio_user_dev.c
> index 6871cd4..529b3d7 100644
> --- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
> +++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c
> @@ -362,6 +362,12 @@ virtio_user_dev_init(struct virtio_user_dev *dev, char *path, int queues,
>  	/* The backend will not report this feature, we add it explicitly */
>  	dev->device_features |= (1ull << VIRTIO_NET_F_STATUS);
>  
> +	/* TODO: VIRTIO_NET_F_MTU is for QEMU to advertise MTU to both frontend
> +	 * and backend driver. For virtio-user, disable it for now, until we
> +	 * have a parameter to specify the MTU.
> +	 */
> +	dev->device_features &= ~(1ull << VIRTIO_NET_F_MTU);
> +
>  	return 0;
>  }
>  
> -- 
> 2.7.4