Quoting Michael Roth (2017-07-26 20:30:52) > This series was motivated by the discussion in this thread: > > https://www.redhat.com/archives/libvir-list/2017-June/msg01370.html > > The issue this series addresses is that when libvirt unplugs a VFIO PCI > device, > it may attempt to bind the host device back to the host driver when QEMU emits > the DEVICE_DELETED event for the corresponding vfio-pci device. However, the > VFIO group FD is not actually cleaned up until vfio-pci device is *finalized* > by QEMU, whereas the event is emitted earlier during device_unparent. > Depending on the host device and how long certain operations like resetting > the > device might take, this can in result in libvirt trying to rebind the device > back to the host while it is still in use by VFIO, leading to host crashes or > other unexpected behavior. > > In particular, Mellanox CX4 adapters on PowerNV hosts might not be fully > quiesced by vfio-pci's finalize() routine until up to 6s after the > DEVICE_DELETED was emitted, leading to detach-device on the libvirt side > pretty > much always crashing the host. > > Implementing this change requires 2 prereqs to ensure the same information is > available when the DEVICE_DELETED is finally emitted: > > 1) Storing the path in the composition patch, which is addressed by PATCH 1, > which was plucked from another pending series from Greg Kurz: > > https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg07922.html > > since we are now "disconnected" at the time the event is emitted, and > > 2) Deferring qemu_opts_del of the DeviceState->QemuOpts till finalize, since > that is where DeviceState->id is stored. This was actually how it was > done in the past, so PATCH 2 simply reverts the change which moved it to > device_unparent. > > From there it's just a mechanical move of the event from device_unparent to > device_finalize.
Ping. The situation has changed somewhat since original posting as Alex now has a fix on the kernel side for the VFIO issue noted above: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6586b561a91cd80a91c8f107ed0d144feb3eadc2 However, I think this series would still be useful for addressing the issue for hosts using older kernels, and there seems to be general interest from the libvirt side in aligning "DEVICE_DELETED" events with the notion that QEMU is completely finished with a device. Patch 1/3 is also needed for another series that Greg is working on and I don't want to hold that up for this series, so if it's preferred that we just post that patch separately in the meantime please let me know. Thanks! > > hw/core/qdev.c | 30 +++++++++++++++++++----------- > include/hw/qdev-core.h | 1 + > 2 files changed, 20 insertions(+), 11 deletions(-) > >