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Commit 1de1ea7e authored by Christian Borntraeger's avatar Christian Borntraeger
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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: default avatarDavid Hildenbrand <david@redhat.com>
Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Cc: stable@vger.kernel.org # 4.13+
Fixes: 190df4a2 (KVM: s390: CMMA tracking, ESSA emulation, migration mode)
Reviewed-by: default avatarClaudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarCornelia Huck <cohuck@redhat.com>
parent c2cf265d

arch/s390/kvm/kvm-s390.c

+11 −7
Original line number Diff line number Diff line
@@ -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: