KVM: x86: move sev_lock/unlock_vcpus_for_migration to kvm_main.c

Move sev_lock/unlock_vcpus_for_migration to kvm_main and call the
new functions the kvm_lock_all_vcpus/kvm_unlock_all_vcpus
and kvm_lock_all_vcpus_nested.

This code allows to lock all vCPUs without triggering lockdep warning
about reaching MAX_LOCK_DEPTH depth by coercing the lockdep into
thinking that we release all the locks other than vcpu'0 lock
immediately after we take them.

No functional change intended.

Suggested-by: Paolo Bonzini <[email protected]>
Signed-off-by: Maxim Levitsky <[email protected]>

Author: Maxim Levitsky

arch/x86/kvm/svm/sev.c

@@ -1845,63 +1845,6 @@ enum sev_migration_role {
 	SEV_NR_MIGRATION_ROLES,
 };
 
-static int sev_lock_vcpus_for_migration(struct kvm *kvm,
-					enum sev_migration_role role)
-{
-	struct kvm_vcpu *vcpu;
-	unsigned long i, j;
-
-	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (mutex_lock_killable_nested(&vcpu->mutex, role))
-			goto out_unlock;
-
-#ifdef CONFIG_PROVE_LOCKING
-		if (!i)
-			/*
-			 * Reset the role to one that avoids colliding with
-			 * the role used for the first vcpu mutex.
-			 */
-			role = SEV_NR_MIGRATION_ROLES;
-		else
-			mutex_release(&vcpu->mutex.dep_map, _THIS_IP_);
-#endif
-	}
-
-	return 0;
-
-out_unlock:
-
-	kvm_for_each_vcpu(j, vcpu, kvm) {
-		if (i == j)
-			break;
-
-#ifdef CONFIG_PROVE_LOCKING
-		if (j)
-			mutex_acquire(&vcpu->mutex.dep_map, role, 0, _THIS_IP_);
-#endif
-
-		mutex_unlock(&vcpu->mutex);
-	}
-	return -EINTR;
-}
-
-static void sev_unlock_vcpus_for_migration(struct kvm *kvm)
-{
-	struct kvm_vcpu *vcpu;
-	unsigned long i;
-	bool first = true;
-
-	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (first)
-			first = false;
-		else
-			mutex_acquire(&vcpu->mutex.dep_map,
-				      SEV_NR_MIGRATION_ROLES, 0, _THIS_IP_);
-
-		mutex_unlock(&vcpu->mutex);
-	}
-}
-
 static void sev_migrate_from(struct kvm *dst_kvm, struct kvm *src_kvm)
 {
 	struct kvm_sev_info *dst = to_kvm_sev_info(dst_kvm);
@@ -2023,10 +1966,10 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, struct kvm *source_kvm)
 		charged = true;
 	}
 
-	ret = sev_lock_vcpus_for_migration(kvm, SEV_MIGRATION_SOURCE);
+	ret = kvm_lock_all_vcpus_nested(kvm, false, SEV_MIGRATION_SOURCE);
 	if (ret)
 		goto out_dst_cgroup;
-	ret = sev_lock_vcpus_for_migration(source_kvm, SEV_MIGRATION_TARGET);
+	ret = kvm_lock_all_vcpus_nested(source_kvm, false, SEV_MIGRATION_TARGET);
 	if (ret)
 		goto out_dst_vcpu;
 
@@ -2040,9 +1983,9 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, struct kvm *source_kvm)
 	ret = 0;
 
 out_source_vcpu:
-	sev_unlock_vcpus_for_migration(source_kvm);
+	kvm_unlock_all_vcpus(source_kvm);
 out_dst_vcpu:
-	sev_unlock_vcpus_for_migration(kvm);
+	kvm_unlock_all_vcpus(kvm);
 out_dst_cgroup:
 	/* Operates on the source on success, on the destination on failure.  */
 	if (charged)

include/linux/kvm_host.h

@@ -1016,6 +1016,12 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
 
 void kvm_destroy_vcpus(struct kvm *kvm);
 
+int kvm_lock_all_vcpus_nested(struct kvm *kvm, bool trylock, unsigned int role);
+void kvm_unlock_all_vcpus(struct kvm *kvm);
+
+#define kvm_lock_all_vcpus(kvm, trylock) \
+	kvm_lock_all_vcpus_nested(kvm, trylock, 0)
+
 void vcpu_load(struct kvm_vcpu *vcpu);
 void vcpu_put(struct kvm_vcpu *vcpu);
 

virt/kvm/kvm_main.c

@@ -1368,6 +1368,77 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+
+/*
+ * Lock all VM vCPUs.
+ * Can be used nested (to lock vCPUS of two VMs for example)
+ */
+int kvm_lock_all_vcpus_nested(struct kvm *kvm, bool trylock, unsigned int role)
+{
+	struct kvm_vcpu *vcpu;
+	unsigned long i, j;
+
+	lockdep_assert_held(&kvm->lock);
+
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+
+		if (trylock && !mutex_trylock_nested(&vcpu->mutex, role))
+			goto out_unlock;
+		else if (!trylock && mutex_lock_killable_nested(&vcpu->mutex, role))
+			goto out_unlock;
+
+#ifdef CONFIG_PROVE_LOCKING
+		if (!i)
+			/*
+			 * Reset the role to one that avoids colliding with
+			 * the role used for the first vcpu mutex.
+			 */
+			role = MAX_LOCK_DEPTH - 1;
+		else
+			mutex_release(&vcpu->mutex.dep_map, _THIS_IP_);
+#endif
+	}
+
+	return 0;
+
+out_unlock:
+
+	kvm_for_each_vcpu(j, vcpu, kvm) {
+		if (i == j)
+			break;
+
+#ifdef CONFIG_PROVE_LOCKING
+		if (j)
+			mutex_acquire(&vcpu->mutex.dep_map, role, 0, _THIS_IP_);
+#endif
+
+		mutex_unlock(&vcpu->mutex);
+	}
+	return -EINTR;
+}
+EXPORT_SYMBOL_GPL(kvm_lock_all_vcpus_nested);
+
+void kvm_unlock_all_vcpus(struct kvm *kvm)
+{
+	struct kvm_vcpu *vcpu;
+	unsigned long i;
+	bool first = true;
+
+	lockdep_assert_held(&kvm->lock);
+
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		if (first)
+			first = false;
+		else
+			mutex_acquire(&vcpu->mutex.dep_map,
+					MAX_LOCK_DEPTH - 1, 0, _THIS_IP_);
+
+		mutex_unlock(&vcpu->mutex);
+	}
+}
+EXPORT_SYMBOL_GPL(kvm_unlock_all_vcpus);
+
+
 /*
  * Allocation size is twice as large as the actual dirty bitmap size.
  * See kvm_vm_ioctl_get_dirty_log() why this is needed.