On 12/29/21 21:04, Halil Pasic wrote:
On Thu, 21 Oct 2021 11:23:25 -0400 Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:The reason a lockdep splat can occur has to do with the fact that the kvm->lock has to be taken before the vcpu->lock; so, for example, when a secure execution guest is started, you may end up with the following scenario: Interception of PQAP(AQIC) instruction executed on the guest: ------------------------------------------------------------ handle_pqap: matrix_dev->lock kvm_vcpu_ioctl: vcpu_mutex Start of secure execution guest: ------------------------------- kvm_s390_cpus_to_pv: vcpu->mutex kvm_arch_vm_ioctl: kvm->lock Queue is unbound from vfio_ap device driver: ------------------------------------------- kvm->lock vfio_ap_mdev_remove_queue: matrix_dev->lockThe way you describe your scenario is a little ambiguous. It seems you choose a stack-trace like description, in a sense that for example for PQAP: first vcpu->mutex is taken and then matrix_dev->lock but you write the latter first and the former second. I think it is more usual to describe such stuff a a sequence of event in a sense that if A precedes B in the text (from the top towards the bottom), then execution of a A precedes the execution of B in time.
I wrote it the way it is displayed in the lockdep splat trace. I'd be happy to re-arrange it if you'd prefer.
Also you are inconsistent with vcpu_mutex vs vcpu->mutex. I can't say I understand the need for this yet. I have been starring at the end result for a while. Let me see if I can come up with an alternate proposal for some things.
Go for it, and may the force be with you.
Regards, Halil
