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
