Hi Alex, Paolo, As reported by Alex [1], since commit 421cfe6596f6 it is possible for a kvm_put_kvm call to hit a refcount of 0 and trigger kvm_destroy_vm while the vfio group lock is held. However, if this occurs, and the associated group is still in the kvm device list, this thread of execution will attempt to acquire the vfio group lock again, resulting in a deadlock. This series proposes to resolve this by adding a new kvm_put_kvm_async which behaves the same as kvm_put_kvm but, in the case where the refcount hits 0, will use a workqueue to perform the kvm_destroy_vm asynchronously. The fix is provided in 2 patches because s390 PCI passthrough has the same issue, albeit introduced slightly later via a different commit. [1]: https://lore.kernel.org/kvm/20230105150930.6ee65182.alex.williamson@xxxxxxxxxx/ Matthew Rosato (2): KVM: async kvm_destroy_vm for vfio devices KVM: s390: pci: use asyncronous kvm put arch/s390/kvm/pci.c | 8 ++++++-- drivers/gpu/drm/i915/gvt/kvmgt.c | 6 +++++- drivers/s390/crypto/vfio_ap_ops.c | 7 ++++++- include/linux/kvm_host.h | 3 +++ virt/kvm/kvm_main.c | 22 ++++++++++++++++++++++ 5 files changed, 42 insertions(+), 4 deletions(-) -- 2.39.0
