On Fri, Jan 06, 2023, Paolo Bonzini wrote: > On 1/5/23 23:23, Sean Christopherson wrote: > > Ha! Case in point. The aforementioned Xen code blatantly violates KVM's locking > > rules: > > > > - kvm->lock is taken outside vcpu->mutex > > Ouch yeah, that's not salvageable. Anything that takes kvm->lock inside > kvm->srcu transitively has to be taking kvm->lock inside vcpu->mutex as > well. > > In abstract I don't think that "vcpu->mutex inside kvm->lock" would be a > particularly problematic rule; kvm->lock critical sections are much shorter > than vcpu->mutex which covers all of KVM_RUN for example, and that hints at > making vcpu->mutex the *outer* mutex. However, I completely forgot the > sev_lock_vcpus_for_migration case, which is the exception that... well, > disproves the rule. Ya, and there are plenty more instances outside of x86. ARM's vGIC stuff also does similar things, see lock_all_vcpus(). PPC's kvmppc_xive_release() and kvmppc_xics_release(). s390's kvm_s390_cpus_from_pv().
