On Thu, Mar 20, 2025 at 10:19 PM Konstantin Shkolnyy <k...@linux.ibm.com> wrote: > > On 3/19/2025 19:58, Jason Wang wrote: > > Adding Cindy and Eugenio > > > > On Thu, Mar 20, 2025 at 12:34 AM Konstantin Shkolnyy <k...@linux.ibm.com> > > wrote: > >> > >> I’m observing a problem while testing VDPA with Nvidia ConnectX-6 (mlx5) > >> on s390. > >> > >> Upon start, virtio_net_device_realize() tries to set a new MAC address > >> by VHOST_VDPA_SET_CONFIG which doesn’t do anything. > >> > >> Later, the VM gets started and learns about the old address from > >> virtio_net_get_config() which returns whatever VHOST_VDPA_GET_CONFIG > >> returns, unless it's "6 zero bytes", in which case it instead returns > >> the desired new address (and the problem is avoided). > >> > >> Then QEMU again tries to set the new address from vhost_net_start(), now > >> by calling vhost_vdpa_net_load_cmd(...,VIRTIO_NET_CTRL_MAC, > >> VIRTIO_NET_CTRL_MAC_ADDR_SET, ...). This time the new address is > >> successfully programmed into the NIC, but the VM doesn't know about it. > > > > Have you enabled shadow virtqueue? If yes, does it work if you don't do > > that? > > I only run it in the default configuration, which has SVQ enabled. > > >> As it is, the only VDPA scenario that's working for me is: > >> 1) Avoid specifying the MAC address in the "vdpa dev add" command (which > >> will create the "6 zero bytes" condition on the first launch). > >> 2) Keep using the same MAC address for every subsequent VM launch on the > >> same NIC "virtual function" (so that the old and new addresses are the > >> same). > > > > This is the way we currently use it. Is there any limitation of this? > > To be honest, I don't know how severe this limitation is, because I'm > not a sysadmin. The problem is that I was searching www for info on how > to setup VDPA and ended up hitting this bug and investigating it.
Exactly, I think we need to improve the documentation anyhow. > Because the found info sources are variable and some show the address > specified in "vdpa dev add". > Thanks
