Re: [PATCH net-next 8/8] vhost/net: enable gso over UDP tunnel support.

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, May 22, 2025 at 02:43:50PM +0800, kernel test robot wrote:
> Hi Paolo,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on net-next/main]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Paolo-Abeni/virtio-introduce-virtio_features_t/20250521-183700
> base:   net-next/main
> patch link:    https://lore.kernel.org/r/f95716aed2c65d079cdb10518431088f3e103899.1747822866.git.pabeni%40redhat.com
> patch subject: [PATCH net-next 8/8] vhost/net: enable gso over UDP tunnel support.
> config: i386-buildonly-randconfig-001-20250522 (https://download.01.org/0day-ci/archive/20250522/202505221428.67HNn025-lkp@intel.com/config)
> compiler: clang version 20.1.2 (https://github.com/llvm/llvm-project 58df0ef89dd64126512e4ee27b4ac3fd8ddf6247)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250522/202505221428.67HNn025-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202505221428.67HNn025-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> drivers/vhost/net.c:1633:30: warning: shift count >= width of type [-Wshift-count-overflow]
>     1633 |         has_tunnel = !!(features & (VIRTIO_BIT(VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO) |
>          |                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    include/linux/virtio_features.h:18:24: note: expanded from macro 'VIRTIO_BIT'
>       18 | #define VIRTIO_BIT(b)           BIT_ULL(b)
>          |                                 ^~~~~~~~~~
>    include/vdso/bits.h:8:30: note: expanded from macro 'BIT_ULL'
>        8 | #define BIT_ULL(nr)             (ULL(1) << (nr))
>          |                                         ^  ~~~~
>    drivers/vhost/net.c:1634:9: warning: shift count >= width of type [-Wshift-count-overflow]
>     1634 |                                     VIRTIO_BIT(VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO)));
>          |                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


yep, this is why I suggested making VIRTIO_BIT(any value > 63) simply 0 on 32 bit.

>    include/linux/virtio_features.h:18:24: note: expanded from macro 'VIRTIO_BIT'
>       18 | #define VIRTIO_BIT(b)           BIT_ULL(b)
>          |                                 ^~~~~~~~~~
>    include/vdso/bits.h:8:30: note: expanded from macro 'BIT_ULL'
>        8 | #define BIT_ULL(nr)             (ULL(1) << (nr))
>          |                                         ^  ~~~~
>    2 warnings generated.
> 
> 
> vim +1633 drivers/vhost/net.c
> 
>   1622	
>   1623	static int vhost_net_set_features(struct vhost_net *n, virtio_features_t features)
>   1624	{
>   1625		size_t vhost_hlen, sock_hlen, hdr_len;
>   1626		bool has_tunnel;
>   1627		int i;
>   1628	
>   1629		hdr_len = (features & ((1ULL << VIRTIO_NET_F_MRG_RXBUF) |
>   1630				       (1ULL << VIRTIO_F_VERSION_1))) ?
>   1631				sizeof(struct virtio_net_hdr_mrg_rxbuf) :
>   1632				sizeof(struct virtio_net_hdr);
> > 1633		has_tunnel = !!(features & (VIRTIO_BIT(VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO) |
>   1634					    VIRTIO_BIT(VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO)));
>   1635		hdr_len += has_tunnel ? sizeof(struct virtio_net_hdr_tunnel) : 0;
>   1636		if (features & (1 << VHOST_NET_F_VIRTIO_NET_HDR)) {
>   1637			/* vhost provides vnet_hdr */
>   1638			vhost_hlen = hdr_len;
>   1639			sock_hlen = 0;
>   1640		} else {
>   1641			/* socket provides vnet_hdr */
>   1642			vhost_hlen = 0;
>   1643			sock_hlen = hdr_len;
>   1644		}
>   1645		mutex_lock(&n->dev.mutex);
>   1646		if ((features & (1 << VHOST_F_LOG_ALL)) &&
>   1647		    !vhost_log_access_ok(&n->dev))
>   1648			goto out_unlock;
>   1649	
>   1650		if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
>   1651			if (vhost_init_device_iotlb(&n->dev))
>   1652				goto out_unlock;
>   1653		}
>   1654	
>   1655		for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
>   1656			mutex_lock(&n->vqs[i].vq.mutex);
>   1657			n->vqs[i].vq.acked_features = features;
>   1658			n->vqs[i].vhost_hlen = vhost_hlen;
>   1659			n->vqs[i].sock_hlen = sock_hlen;
>   1660			mutex_unlock(&n->vqs[i].vq.mutex);
>   1661		}
>   1662		mutex_unlock(&n->dev.mutex);
>   1663		return 0;
>   1664	
>   1665	out_unlock:
>   1666		mutex_unlock(&n->dev.mutex);
>   1667		return -EFAULT;
>   1668	}
>   1669	
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki