Messages in this thread | | | From | Peter Gonda <> | Date | Tue, 26 Apr 2022 13:06:57 -0600 | Subject | Re: [PATCH v3] KVM: SEV: Mark nested locking of vcpu->lock |
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On Thu, Apr 21, 2022 at 9:56 AM Paolo Bonzini <pbonzini@redhat.com> wrote: > > On 4/20/22 22:14, Peter Gonda wrote: > >>>> svm_vm_migrate_from() uses sev_lock_vcpus_for_migration() to lock all > >>>> source and target vcpu->locks. Mark the nested subclasses to avoid false > >>>> positives from lockdep. > >> Nope. Good catch, I didn't realize there was a limit 8 subclasses: > > Does anyone have thoughts on how we can resolve this vCPU locking with > > the 8 subclass max? > > The documentation does not have anything. Maybe you can call > mutex_release manually (and mutex_acquire before unlocking). > > Paolo
Hmm this seems to be working thanks Paolo. To lock I have been using:
... if (mutex_lock_killable_nested( &vcpu->mutex, i * SEV_NR_MIGRATION_ROLES + role)) goto out_unlock; mutex_release(&vcpu->mutex.dep_map, _THIS_IP_); ...
To unlock: ... mutex_acquire(&vcpu->mutex.dep_map, 0, 0, _THIS_IP_); mutex_unlock(&vcpu->mutex); ...
If I understand correctly we are fully disabling lockdep by doing this. If this is the case should I just remove all the '_nested' usage so switch to mutex_lock_killable() and remove the per vCPU subclass?
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