On Tue, Jan 31, 2023 at 10:00:14AM -0500, Matthew Rosato wrote: > On 1/31/23 9:48 AM, Jason Gunthorpe wrote: > > On Tue, Jan 31, 2023 at 09:46:18AM -0500, Anthony Krowiak wrote: > > > >>> Maybe you should split that lock and have a dedicated apcb lock? > >> > >> I don't think that would suffice for taking the vCPUs out of SIE. > > > > Then I think we have to keep this patch and also do Matthew's patch to > > keep kvm refs inside vfio as well. > > > > I don't think keeping kvm refs inside vfio solves this issue though > -- Even if we handle the kvm_put_kvm asynchronously within vfio as > previously proposed, kvm_vfio_release will eventually get called and > it gets called with the kvm->lock already held, then proceeds to > call vfio_file_set_kvm which gets the group->lock. That order > conflicts with the hierarchy used by the driver during open_device > of vfio->group_lock ... kvm->lock. The group lock is held by vfio_file_set_kvm() only because we don't have a refcount and we have to hold it across the open call to keep the pointer alive. With proper refcounting you'd split this to a spinlock and hold it only while obtaining the get ref for the open thread. Jason
