| Message ID | 20220404194605.1569855-1-pgonda@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: SEV: Mark nested locking of vcpu->lock | expand |
> > This is rather gross, and I'm guessing it adds extra work for the non-lockdep > case, assuming the compiler isn't so clever that it can figure out that the result > is never used. Not that this is a hot path... > > Does each lock actually need a separate subclass? If so, why don't the other > paths that lock all vCPUs complain? > > If differentiating the two VMs is sufficient, then we can pass in SINGLE_DEPTH_NESTING > for the second round of locks. If a per-vCPU subclass is required, we can use the > vCPU index and assign evens to one and odds to the other, e.g. this should work and > compiles to a nop when LOCKDEP is disabled (compile tested only). It's still gross, > but we could pretty it up, e.g. add defines for the 0/1 param. I checked and the perf vCPU subclassing is required. If I just only use a SINGLE_DEPTH_NESTING on the second VM's vCPUs I still see the warning. This odds and evens approach seems much better. I'll update to use that in the V2 unless there is a better idea.
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 75fa6dd268f0..8f77421c1c4b 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1591,15 +1591,16 @@ static void sev_unlock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm) atomic_set_release(&src_sev->migration_in_progress, 0); } - -static int sev_lock_vcpus_for_migration(struct kvm *kvm) +static int sev_lock_vcpus_for_migration(struct kvm *kvm, unsigned int *subclass) { struct kvm_vcpu *vcpu; unsigned long i, j; kvm_for_each_vcpu(i, vcpu, kvm) { - if (mutex_lock_killable(&vcpu->mutex)) + if (mutex_lock_killable_nested(&vcpu->mutex, *subclass)) goto out_unlock; + + ++(*subclass); } return 0; @@ -1717,6 +1718,7 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd) struct kvm *source_kvm; bool charged = false; int ret; + unsigned int vcpu_mutex_subclass = 0; source_kvm_file = fget(source_fd); if (!file_is_kvm(source_kvm_file)) { @@ -1745,10 +1747,10 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd) charged = true; } - ret = sev_lock_vcpus_for_migration(kvm); + ret = sev_lock_vcpus_for_migration(kvm, &vcpu_mutex_subclass); if (ret) goto out_dst_cgroup; - ret = sev_lock_vcpus_for_migration(source_kvm); + ret = sev_lock_vcpus_for_migration(source_kvm, &vcpu_mutex_subclass); if (ret) goto out_dst_vcpu;
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. Fixes: b56639318bb2b ("KVM: SEV: Add support for SEV intra host migration") Reported-by: John Sperbeck<jsperbeck@google.com> Suggested-by: David Rientjes <rientjes@google.com> Signed-off-by: Peter Gonda <pgonda@google.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Sean Christopherson <seanjc@google.com> Cc: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- Tested by running sev_migrate_tests with lockdep enabled. Before we see a warning from sev_lock_vcpus_for_migration(). After we get no warnings. --- arch/x86/kvm/svm/sev.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)