KVM: s390: add proper locking for CMMA migration bitmap

Some parts of the cmma migration bitmap is already protected
with the kvm->lock (e.g. the migration start). On the other
hand the read of the cmma bits is not protected against a
concurrent free, neither is the emulation of the ESSA instruction.
Let's extend the locking to all related ioctls by using
the slots lock for
- kvm_s390_vm_start_migration
- kvm_s390_vm_stop_migration
- kvm_s390_set_cmma_bits
- kvm_s390_get_cmma_bits

In addition to that, we use synchronize_srcu before freeing
the migration structure as all users hold kvm->srcu for read.
(e.g. the ESSA handler).

Reported-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: stable@vger.kernel.org # 4.13+
Fixes: 190df4a212a7 (KVM: s390: CMMA tracking, ESSA emulation, migration mode)
Reviewed-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>

1 files changed, 11 insertions, 7 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index abcd24fdde3f..52880e980a33 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -766,7 +766,7 @@ static void kvm_s390_sync_request_broadcast(struct kvm *kvm, int req)
 
 /*
  * Must be called with kvm->srcu held to avoid races on memslots, and with
- * kvm->lock to avoid races with ourselves and kvm_s390_vm_stop_migration.
+ * kvm->slots_lock to avoid races with ourselves and kvm_s390_vm_stop_migration.
  */
 static int kvm_s390_vm_start_migration(struct kvm *kvm)
 {
@@ -822,7 +822,7 @@ static int kvm_s390_vm_start_migration(struct kvm *kvm)
 }
 
 /*
- * Must be called with kvm->lock to avoid races with ourselves and
+ * Must be called with kvm->slots_lock to avoid races with ourselves and
  * kvm_s390_vm_start_migration.
  */
 static int kvm_s390_vm_stop_migration(struct kvm *kvm)
@@ -837,6 +837,8 @@ static int kvm_s390_vm_stop_migration(struct kvm *kvm)
 
         if (kvm->arch.use_cmma) {
                 kvm_s390_sync_request_broadcast(kvm, KVM_REQ_STOP_MIGRATION);
+                /* We have to wait for the essa emulation to finish */
+                synchronize_srcu(&kvm->srcu);
                 vfree(mgs->pgste_bitmap);
         }
         kfree(mgs);
@@ -846,14 +848,12 @@ static int kvm_s390_vm_stop_migration(struct kvm *kvm)
 static int kvm_s390_vm_set_migration(struct kvm *kvm,
                                      struct kvm_device_attr *attr)
 {
-        int idx, res = -ENXIO;
+        int res = -ENXIO;
 
-        mutex_lock(&kvm->lock);
+        mutex_lock(&kvm->slots_lock);
         switch (attr->attr) {
         case KVM_S390_VM_MIGRATION_START:
-                idx = srcu_read_lock(&kvm->srcu);
                 res = kvm_s390_vm_start_migration(kvm);
-                srcu_read_unlock(&kvm->srcu, idx);
                 break;
         case KVM_S390_VM_MIGRATION_STOP:
                 res = kvm_s390_vm_stop_migration(kvm);
@@ -861,7 +861,7 @@ static int kvm_s390_vm_set_migration(struct kvm *kvm,
         default:
                 break;
         }
-        mutex_unlock(&kvm->lock);
+        mutex_unlock(&kvm->slots_lock);
 
         return res;
 }
@@ -1751,7 +1751,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
                 r = -EFAULT;
                 if (copy_from_user(&args, argp, sizeof(args)))
                         break;
+                mutex_lock(&kvm->slots_lock);
                 r = kvm_s390_get_cmma_bits(kvm, &args);
+                mutex_unlock(&kvm->slots_lock);
                 if (!r) {
                         r = copy_to_user(argp, &args, sizeof(args));
                         if (r)
@@ -1765,7 +1767,9 @@ long kvm_arch_vm_ioctl(struct file *filp,
                 r = -EFAULT;
                 if (copy_from_user(&args, argp, sizeof(args)))
                         break;
+                mutex_lock(&kvm->slots_lock);
                 r = kvm_s390_set_cmma_bits(kvm, &args);
+                mutex_unlock(&kvm->slots_lock);
                 break;
         }
         default: