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Tsirkin" , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , si-wei.liu@oracle.com, Jiri Pirko , virtualization@lists.linux.dev, linux-kernel@vger.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> Content-Language: en-US From: Dragos Tatulea In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR3P281CA0097.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:a1::15) To DS0PR12MB8295.namprd12.prod.outlook.com (2603:10b6:8:f6::21) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8304:EE_|PH7PR12MB7332:EE_ X-MS-Office365-Filtering-Correlation-Id: 33e35b90-c355-4ce0-42cd-08dcc8d83102 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014; 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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? I see that .set_config() is called during boot time. CVQ commands are happening only when the MAC is configured from within the VM. > Usually, we don't recommend using the set_config() function because > the configuration space should be read-only for modern devices. > Ack > 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 for the clarification. So if I understand correctly, there will be no way for qemu to set a random MAC address for vdpa devices going forward. Unless it is done through the CVQ from within the VM. Thanks, Dragos