On Tue, 2011-08-23 at 15:14 +0200, Roedel, Joerg wrote: > On Mon, Aug 22, 2011 at 03:17:00PM -0400, Alex Williamson wrote: > > On Mon, 2011-08-22 at 19:25 +0200, Joerg Roedel wrote: > > > > I am in favour of /dev/vfio/$GROUP. If multiple devices should be > > > assigned to a guest, there can also be an ioctl to bind a group to an > > > address-space of another group (certainly needs some care to not allow > > > that both groups belong to different processes). > > > > That's an interesting idea. Maybe an interface similar to the current > > uiommu interface, where you open() the 2nd group fd and pass the fd via > > ioctl to the primary group. IOMMUs that don't support this would fail > > the attach device callback, which would fail the ioctl to bind them. It > > will need to be designed so any group can be removed from the super-set > > and the remaining group(s) still works. This feels like something that > > can be added after we get an initial implementation. > > Handling it through fds is a good idea. This makes sure that everything > belongs to one process. I am not really sure yet if we go the way to > just bind plain groups together or if we create meta-groups. The > meta-groups thing seems somewhat cleaner, though. I'm leaning towards binding because we need to make it dynamic, but I don't really have a good picture of the lifecycle of a meta-group. > > > Btw, a problem we havn't talked about yet entirely is > > > driver-deassignment. User space can decide to de-assign the device from > > > vfio while a fd is open on it. With PCI there is no way to let this fail > > > (the .release function returns void last time i checked). Is this a > > > problem, and yes, how we handle that? > > > > The current vfio has the same problem, we can't unbind a device from > > vfio while it's attached to a guest. I think we'd use the same solution > > too; send out a netlink packet for a device removal and have the .remove > > call sleep on a wait_event(, refcnt == 0). We could also set a timeout > > and SIGBUS the PIDs holding the device if they don't return it > > willingly. Thanks, > > Putting the process to sleep (which would be uninterruptible) seems bad. > The process would sleep until the guest releases the device-group, which > can take days or months. > The best thing (and the most intrusive :-) ) is to change PCI core to > allow unbindings to fail, I think. But this probably further complicates > the way to upstream VFIO... Yes, it's not ideal but I think it's sufficient for now and if we later get support for returning an error from release, we can set a timeout after notifying the user to make use of that. Thanks, Alex -- 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
