[PATCH] KVM: SEV: Mark nested locking of vcpu->lock

[Peter Gonda]

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@xxxxxxxxxx>
Suggested-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---

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(-)

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;
 
-- 
2.35.1.1094.g7c7d902a7c-goog