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Tsirkin" To: Cindy Lu Cc: Dragos Tatulea , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , si-wei.liu@oracle.com, Jiri Pirko , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] vdpa/mlx5: Use random MAC address when no nic vport MAC set Message-ID: <20240901144739-mutt-send-email-mst@kernel.org> References: <20240827160256.2446626-2-dtatulea@nvidia.com> <8daf221f-8d87-4da1-944c-3bcd0edea604@nvidia.com> <55b7ae23-6000-4699-9bac-5e72fbdcd803@nvidia.com> <0648a9d9-a056-4cdb-bfb8-a792bce1e771@nvidia.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Fri, Aug 30, 2024 at 05:29:14PM +0800, Cindy Lu wrote: > On Fri, 30 Aug 2024 at 03:03, Dragos Tatulea wrote: > > > > > > > > On 29.08.24 12:00, Dragos Tatulea wrote: > > > > > > > > > On 29.08.24 11:05, Cindy Lu wrote: > > >> On Wed, 28 Aug 2024 at 17:37, Dragos Tatulea wrote: > > >>> > > >>> > > >>> > > >>> On 28.08.24 11:00, Cindy Lu wrote: > > >>>> On Wed, 28 Aug 2024 at 09:51, Jason Wang wrote: > > >>>>> > > >>>>> On Wed, Aug 28, 2024 at 12:03 AM Dragos Tatulea 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 > > >>>>>> Reviewed-by: Jiri Pirko > > >>>>> > > >>>>> Acked-by: Jason Wang > > >>>>> > > >>>>> (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@redhat.com/ > > >>>> 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. > > (Side note) > > While looking at another issue I discovered that it's possible to > > configure a random MAC on the mlx5_vdpa device at VM boot time if > > device MAC configuration is implemented during during .set_config(). So > > I was able to boot up a VM with a random MAC address coming from qemu > > and the traffic worked with this new MAC. > > > > So now I'm not sure if this is just by luck or if the .set_config() > > op should be implemented for the MAC part in our device. > > > > Thanks, > > Dragos > > > Hi Dragos， > For qemu part, I think this is not set from set_config()? it should > be from the CVQ? You are confusing two things. Provisioning is not through CVQ. > Usually, we don't recommend using the set_config() function because > the configuration space should be read-only for modern devices. > > Now there is a bug in this part of qemu, and we plan to remove the > code to set_config() in virtio_net_device_realize(), here is the patch > https://lore.kernel.org/all/CACGkMEvCSKfahpBQLAMmSzdFN-QPhg5Zx+UQVrFX0HsWybZZNA@mail.gmail.com/T/ > and this is still under review > > thanks > cindy