On Fri, 30 Aug 2024 at 22:46, Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > > Hi Cindy, > > On 30.08.24 15:52, Dragos Tatulea wrote: > > > > > > On 30.08.24 11:12, Cindy Lu wrote: > >> On Thu, 29 Aug 2024 at 18:00, Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > >>> > >>> > >>> > >>> On 29.08.24 11:05, Cindy Lu wrote: > >>>> On Wed, 28 Aug 2024 at 17:37, Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > >>>>> > >>>>> > >>>>> > >>>>> On 28.08.24 11:00, Cindy Lu wrote: > >>>>>> On Wed, 28 Aug 2024 at 09:51, Jason Wang <jasowang@xxxxxxxxxx> wrote: > >>>>>>> > >>>>>>> On Wed, Aug 28, 2024 at 12:03 AM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote: > >>>>>>>> > >>>>>>>> When the vdpa device is configured without a specific MAC > >>>>>>>> address, the vport MAC address is used. However, this > >>>>>>>> address can be 0 which prevents the driver from properly > >>>>>>>> configuring the MPFS and breaks steering. > >>>>>>>> > >>>>>>>> The solution is to simply generate a random MAC address > >>>>>>>> when no MAC is set on the nic vport. > >>>>>>>> > >>>>>>>> Now it's possible to create a vdpa device without a > >>>>>>>> MAC address and run qemu with this device without needing > >>>>>>>> to configure an explicit MAC address. > >>>>>>>> > >>>>>>>> Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx> > >>>>>>>> Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx> > >>>>>>> > >>>>>>> Acked-by: Jason Wang <jasowang@xxxxxxxxxx> > >>>>>>> > >>>>>>> (Adding Cindy for double checking if it has any side effect on Qemu side) > >>>>>>> > >>>>>>> Thanks > >>>>>>> > >>>>>> But Now there is a bug in QEMU: if the hardware MAC address does not > >>>>>> match the one in the QEMU command line, it will cause traffic loss. > >>>>>> > >>>>> Why is this a new issue in qemu? qemu in it's current state won't work > >>>>> with a different mac address that the one that is set in HW anyway. > >>>>> > >>>> this is not a new bug. We are trying to fix it because it will cause > >>>> traffic lose without any warning. > >>>> in my fix , this setting (different mac in device and Qemu) will fail > >>>> to load the VM. > >>> Which is a good thing, right? Some feedback to the user that there is > >>> a misconfig. I got bitten by this so many times... Thank you for adding it. > >>> > >>>> > >>>>>> So, Just an FYI here: if your patch merged, it may cause traffic loss. > >>>>>> and now I'm working in the fix it in qemu, the link is > >>>>>> https://patchew.org/QEMU/20240716011349.821777-1-lulu@xxxxxxxxxx/ > >>>>>> The idea of this fix is > >>>>>> There are will only two acceptable situations for qemu: > >>>>>> 1. The hardware MAC address is the same as the MAC address specified > >>>>>> in the QEMU command line, and both MAC addresses are not 0. > >>>>>> 2. The hardware MAC address is not 0, and the MAC address in the QEMU > >>>>>> command line is 0. In this situation, the hardware MAC address will > >>>>>> overwrite the QEMU command line address. > >>>>>> > >>>>> Why would this not work with this patch? This patch simply sets a MAC > >>>>> if the vport doesn't have one set. Which allows for more scenarios to > >>>>> work. > >>>>> > >>>> I do not mean your patch will not work, I just want to make some > >>>> clarify here.Your patch + my fix may cause the VM to fail to load in > >>>> some situations, and this is as expected. > >>>> Your patch is good to merge. > >>> Ack. Thank you for the clarification. > >>> > >>> Thanks, > >>> Dragos > >>> > >> Hi Dragos， > >> I think we need to hold this patch. Because it may not be working > >> with upstream qemu. > >> > >> MLX will create a random MAC address for your patch. Additionally, if > >> there is no specific MAC in the QEMU command line, QEMU will also > >> generate a random MAC. > >> these two MAC are not the same. and this will cause traffic loss. > > Ahaa, it turns out that qemu 8.x and 9.x have different behaviour. > > > > Initially I was testing this scenario (vdpa device created with no mac > > and no mac set in qemu cli) with qemu 8.x. There, qemu was not being > > able to set the qemu generated random mac addres because .set_config() > > is a nop in mlx5_vdpa. > > > > Then I moved to qemu 9.x and saw that this scenario was working because > > now the CVQ was used instead to configure the mac on the device. > > > > So this patch should definitely not be applied. > > > > I was thinking if there are ways to fix this for 8.x. The only feasible > > way is to implement .set_config() in mlx5_vdpa for the mac > > configuration. But as you previousy said, this is discouraged. > > > I just tested your referenced qemu fix from patchwork and I found that > for the case when a vdpa device doesn't have a mac address (mac address > 0 and VIRTIO_NET_F_MAC not set) qemu will return an error. So with this > fix we'd be back to square one where the user always has to set a mac > somewhere. > > Would it be possible to take this case into consideration with your > fix? > > Thanks, > Dragos > Hi Dragos Thanks for your test and help, I think I can add a check for VIRTIO_NET_F_MAC in the qemu code. if the device's Mac is 0 and the VIRTIO_NET_F_MAC is not set. The guest VM will fail to load. I will double-check this Thanks Cindy
