On Sun, Apr 23, 2023 at 07:52:10AM +0000, Alvaro Karsz wrote: > > Hmm. I was wrong. There is no way to disable CVQ feature bit. > > > > 1. Reset the device. > > 2. Set the ACKNOWLEDGE status bit: the guest OS has notice the device. > > 3. Set the DRIVER status bit: the guest OS knows how to drive the device. > > 4. Read device feature bits, and write the subset of feature bits > > understood by the OS and driver to the > > device. During this step the driver MAY read (but MUST NOT write) the > > device-specific configuration > > fields to check that it can support the device before accepting it. > > 5. Set the FEATURES_OK status bit. The driver MUST NOT accept new feature > > bits after this step. > > 6. Re-read device status to ensure the FEATURES_OK bit is still set: > > otherwise, the device does not > > support our subset of features and the device is unusable. > > 7. Perform device-specific setup, including discovery of virtqueues for the > > device, optional per-> bus setup, > > reading and possibly writing the device’s virtio configuration space, and > > population of virtqueues. > > 8. Set the DRIVER_OK status bit. At this point the device is “live”. > > > > > > So features are confirmed before find vqs. > > > > The rest of stuff can probably just be moved to after find_vqs without > > much pain. > > > Actually, I think that with a little bit of pain :) > If we use small vrings and a GRO feature bit is set, Linux will need to > allocate 64KB of continuous memory for every receive descriptor..
Oh right. Hmm. Well this is same as big packets though, isn't it? > Instead of failing probe if GRO/CVQ are set, can we just reset the device if > we discover small vrings and start over? > Can we remember that this device uses small vrings, and then just avoid > negotiating the features that we cannot support? We technically can of course. I am just not sure supporting CVQ with just 1 s/g entry will ever be viable. -- MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
