On Sun, 2011-08-14 at 12:23 +0930, Rusty Russell wrote: > On Sat, 13 Aug 2011 11:51:01 +0300, Sasha Levin <levinsasha928@xxxxxxxxx> wrote: > > The MAC of a virtio-net device is located at the first field of the device > > specific header. This header is located at offset 20 if the device doesn't > > support MSI-X or offset 24 if it does. > > Erk. This means, in general, we have to do virtio_find_single_vq or > config->find_vqs before we examine any config options. > > Look at virtio_blk, which has the same error. > > Solutions in order of best to worst: > (1) Enable MSI-X before calling device probe. This means reserving two > vectors in virtio_pci_probe to ensure we *can* do this, I think. Michael? Do you mean reserving the vectors even before we probed the device for MSI-X support? Wouldn't we need 3 vectors then? (config, input, output). > (2) Ensure ordering of "find_vqs then access config space" statically. This > probably means handing the vqs array to virtio_config_val, so noone > can call it before they have their virtqueues. Just noticed that only virtio-blk uses virtio_config_val(), while the others are still doing 'if(virtio_has_feature()) vdev->config->get()', I'll send patches to fix that regardless of what we end up doing here. Did you want to pass the vq array to virtio_config_val() just to check that they were already found? > (3) Ensure ordering dynamically, ie. BUG_ON() if they haven't done > find_vqs when they call the config accessors. > > If (1) is too invasive for -stable, then we should rearrange the drivers > in separate patches (and cc: -stable), then fix it properly. > > Good catch Sasha! > > Cheers, > Rusty. -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
