On Fri, Mar 21, 2025 at 12:29 PM Konstantin Shkolnyy <k...@linux.ibm.com> wrote: > > On 3/20/2025 20:22, Jason Wang wrote: > > On Fri, Mar 21, 2025 at 12:45 AM Konstantin Shkolnyy <k...@linux.ibm.com> > > wrote: > >> > >> On 3/19/2025 19:58, Jason Wang wrote: > >>> On Thu, Mar 20, 2025 at 12:34 AM Konstantin Shkolnyy <k...@linux.ibm.com> > >>> wrote: > >>>> Upon reading this forum, I see that VHOST_VDPA_SET_CONFIG is > >>>> “deprecated”, and so VIRTIO_NET_CTRL_MAC_ADDR_SET must be the right > >>>> method, but it’s apparently called too late. > >>> > >>> VHOST_VDPA_SET_CONFIG requires the vDPA parent support which is not > >>> necessarily there. > >> > >> The mlx5 driver doesn't do anything for VHOST_VDPA_SET_CONFIG. Intel's > >> driver, however, apparently stores the configuration. So, it appears, > >> Intel will avoid the problem... Perhaps mlx5 could do the same so that > >> QEMU can set the address before it starts the VM (QEMU doesn't have to > >> later let the VM change the config). > > > > The problem is that config space is not allowed to be written, that is > > why mlx5 doesn't implement the write method. > > > >> Conceptually, setting the address > >> by QEMU cmdline doesn't look different from setting it by "vdpa dev add". > > > > It's kind of different. > > > > E.g the device may not even have VIRTIO_NET_F_MAC feature etc. > > I'm not sure I understand... This is the MAC address returned by > VHOST_VDPA_GET_CONFIG. If mlx5 allows it to be set by "vdpa dev add", > shouldn't it also allow it to be set by VHOST_VDPA_SET_CONFIG called by > virtio_net_device_realize(), before the VM exists. > > When VM starts running, it queries this MAC address and QEMU fetches it > by VHOST_VDPA_GET_CONFIG. But, because VHOST_VDPA_SET_CONFIG hasn't > stored it, it fetches a wrong stale address. > Hi Konstantin This buggy process is functioning in the MLX driver as follow steps
0: kernel creates VDPA device [MLX: if the mac was not set while creating, the mac is 0 in hardware] 1. Get Mac from the cmd line.if the cmdline is 0, qemu will create a random mac address, save it in VirtIONet->mac and VirtIONet->nic_conf.macaddr 3. qemu called virtio_net_device_realize() in this function, the mac address in VirtIONet->mac will set to kernel while calling vhost_net_set_config() [ MLX not supported ] 4. qemu boot called vhost_net_get_config, get the hardware mac address and saved in VirtIONet->nic_conf.macaddr this will read the mac from the kernel and change the mac address to kernel's mac [ for MLX, if the hardware mac is 0, using the cmdline mac(or random mac ) ] NOTE the information in VirtIONet->mac was not change 5, the qemu will call vhost_vdpa_net_cvq_load(). Even if the cvq/svq not enabled in qemu cmdline this function will set the mac in VirtIONet->mac to the kernel.[mlx support] This will result in QEMU's MAC address differing from the hardware's MAC address. So our fix is 1. Add a tool for users to set the MAC address before QEMU loads. 2. Include a parameter in QEMU to check the MAC address before booting; QEMU will fail to load the system if the MAC addresses do not match. Thanks Cindy
