Re: [PATCH v7 5/6] KVM: x86: Refactor tsc synchronization code
From: Paolo Bonzini <pbonzini@redhat.com>
Date: 2021-09-24 09:31:21
Also in:
kvm, kvmarm
On 02/09/21 21:21, Sean Christopherson wrote:
quoted
+ if (!matched) { + ... + spin_lock(&kvm->arch.pvclock_gtod_sync_lock); + kvm->arch.nr_vcpus_matched_tsc = 0; + } else if (!already_matched) { + spin_lock(&kvm->arch.pvclock_gtod_sync_lock); + kvm->arch.nr_vcpus_matched_tsc++; + } + + kvm_track_tsc_matching(vcpu); + spin_unlock(&kvm->arch.pvclock_gtod_sync_lock);This unlock is imbalanced if matched and already_matched are both true. It's not immediately obvious that that_can't_ happen, and if it truly can't happen then conditionally locking is pointless (because it's not actually conditional).
This is IMO another reason to unify tsc_write_lock and pvclock_gtod_sync_lock. The chances of contention are pretty slim. As soon as I sort out the next -rc3 pull request I'll send out my version of Oliver's patches. Thanks, Paolo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel