Re: [PATCH v4] vfio: fix potential deadlock on vfio group lock

Jason Gunthorpe
2023-01-16T15:16:20Z

On Fri, Jan 13, 2023 at 07:03:51PM -0500, Matthew Rosato wrote:
> Currently it is possible that the final put of a KVM reference comes from
> vfio during its device close operation. This occurs while the vfio group
> lock is held; however, if the vfio device is still in the kvm device list,
> then the following call chain could result in a deadlock:
>
> kvm_put_kvm
> -> kvm_destroy_vm
> -> kvm_destroy_devices
> -> kvm_vfio_destroy
> -> kvm_vfio_file_set_kvm
> -> vfio_file_set_kvm
> -> group->group_lock/group_rwsem
>
> Avoid this scenario by having vfio core code acquire a KVM reference
> the first time a device is opened and hold that reference until right
> after the group lock is released after the last device is closed.
>
> Fixes: 421cfe6596f6 ("vfio: remove VFIO_GROUP_NOTIFY_SET_KVM")
> Reported-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason