Re: [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Tony Krowiak <akrowiak@linux.ibm.com>]

On 5/19/22 2:33 PM, Matthew Rosato wrote:
> Rather than relying on a notifier for associating the KVM with
> the group, let's assume that the association has already been
> made prior to device_open.  The first time a device is opened
> associate the group KVM with the device.
>
> This fixes a user-triggerable oops in GVT.
>
> Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
>   drivers/gpu/drm/i915/gvt/gtt.c        |  4 +-
>   drivers/gpu/drm/i915/gvt/gvt.h        |  3 -
>   drivers/gpu/drm/i915/gvt/kvmgt.c      | 82 ++++++--------------------
>   drivers/s390/crypto/vfio_ap_ops.c     | 35 ++---------
>   drivers/s390/crypto/vfio_ap_private.h |  3 -
>   drivers/vfio/vfio.c                   | 83 ++++++++++-----------------
>   include/linux/vfio.h                  |  6 +-
>   7 files changed, 57 insertions(+), 159 deletions(-)
>
>
>   
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index e8914024f5b1..a7d2a95796d3 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1284,25 +1284,6 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
>   	}
>   }
>   
> -static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
> -				       unsigned long action, void *data)
> -{
> -	int notify_rc = NOTIFY_OK;
> -	struct ap_matrix_mdev *matrix_mdev;
> -
> -	if (action != VFIO_GROUP_NOTIFY_SET_KVM)
> -		return NOTIFY_OK;
> -
> -	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
> -
> -	if (!data)
> -		vfio_ap_mdev_unset_kvm(matrix_mdev);
> -	else if (vfio_ap_mdev_set_kvm(matrix_mdev, data))
> -		notify_rc = NOTIFY_DONE;
> -
> -	return notify_rc;
> -}
> -
>   static struct vfio_ap_queue *vfio_ap_find_queue(int apqn)
>   {
>   	struct device *dev;
> @@ -1402,11 +1383,10 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev)
>   	unsigned long events;
>   	int ret;
>   
> -	matrix_mdev->group_notifier.notifier_call = vfio_ap_mdev_group_notifier;
> -	events = VFIO_GROUP_NOTIFY_SET_KVM;
> +	if (!vdev->kvm)
> +		return -EINVAL;
>   
> -	ret = vfio_register_notifier(vdev, VFIO_GROUP_NOTIFY, &events,
> -				     &matrix_mdev->group_notifier);
> +	ret = vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm);
>   	if (ret)
>   		return ret;

I'm sorry I didn't see this with my last review, but maybe move the call
to vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm) after the successful
registration of the IOMMU notifier? This way you won't be plugging AP queues
into the guest only to remove them if the registration fails.

>   
> @@ -1415,12 +1395,11 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev)
>   	ret = vfio_register_notifier(vdev, VFIO_IOMMU_NOTIFY, &events,
>   				     &matrix_mdev->iommu_notifier);
>   	if (ret)
> -		goto out_unregister_group;
> +		goto err_kvm;
>   	return 0;
>   
> -out_unregister_group:
> -	vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
> -				 &matrix_mdev->group_notifier);
> +err_kvm:
> +	vfio_ap_mdev_unset_kvm(matrix_mdev);
>   	return ret;
>   }
>   
> @@ -1431,8 +1410,6 @@ static void vfio_ap_mdev_close_device(struct vfio_device *vdev)
>   
>   	vfio_unregister_notifier(vdev, VFIO_IOMMU_NOTIFY,
>   				 &matrix_mdev->iommu_notifier);
> -	vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
> -				 &matrix_mdev->group_notifier);
>   	vfio_ap_mdev_unset_kvm(matrix_mdev);
>   }
>   
> diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
> index 648fcaf8104a..a26efd804d0d 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -81,8 +81,6 @@ struct ap_matrix {
>    * @node:	allows the ap_matrix_mdev struct to be added to a list
>    * @matrix:	the adapters, usage domains and control domains assigned to the
>    *		mediated matrix device.
> - * @group_notifier: notifier block used for specifying callback function for
> - *		    handling the VFIO_GROUP_NOTIFY_SET_KVM event
>    * @iommu_notifier: notifier block used for specifying callback function for
>    *		    handling the VFIO_IOMMU_NOTIFY_DMA_UNMAP even
>    * @kvm:	the struct holding guest's state
> @@ -94,7 +92,6 @@ struct ap_matrix_mdev {
>   	struct vfio_device vdev;
>   	struct list_head node;
>   	struct ap_matrix matrix;
> -	struct notifier_block group_notifier;
>   	struct notifier_block iommu_notifier;
>   	struct kvm *kvm;
>   	crypto_hook pqap_hook;
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index cfcff7764403..831fc722e3f8 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1083,10 +1083,21 @@ static struct file *vfio_device_open(struct vfio_device *device)
>   
>   	mutex_lock(&device->dev_set->lock);
>   	device->open_count++;
> -	if (device->open_count == 1 && device->ops->open_device) {
> -		ret = device->ops->open_device(device);
> -		if (ret)
> -			goto err_undo_count;
> +	if (device->open_count == 1) {
> +		/*
> +		 * Here we pass the KVM pointer with the group under the read
> +		 * lock.  If the device driver will use it, it must obtain a
> +		 * reference and release it during close_device.
> +		 */
> +		down_read(&device->group->group_rwsem);
> +		device->kvm = device->group->kvm;
> +
> +		if (device->ops->open_device) {
> +			ret = device->ops->open_device(device);
> +			if (ret)
> +				goto err_undo_count;
> +		}
> +		up_read(&device->group->group_rwsem);
>   	}
>   	mutex_unlock(&device->dev_set->lock);
>   
> @@ -1119,10 +1130,14 @@ static struct file *vfio_device_open(struct vfio_device *device)
>   
>   err_close_device:
>   	mutex_lock(&device->dev_set->lock);
> +	down_read(&device->group->group_rwsem);
>   	if (device->open_count == 1 && device->ops->close_device)
>   		device->ops->close_device(device);
>   err_undo_count:
>   	device->open_count--;
> +	if (device->open_count == 0 && device->kvm)
> +		device->kvm = NULL;
> +	up_read(&device->group->group_rwsem);
>   	mutex_unlock(&device->dev_set->lock);
>   	module_put(device->dev->driver->owner);
>   err_unassign_container:
> @@ -1315,9 +1330,13 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
>   
>   	mutex_lock(&device->dev_set->lock);
>   	vfio_assert_device_open(device);
> +	down_read(&device->group->group_rwsem);
>   	if (device->open_count == 1 && device->ops->close_device)
>   		device->ops->close_device(device);
> +	up_read(&device->group->group_rwsem);
>   	device->open_count--;
> +	if (device->open_count == 0)
> +		device->kvm = NULL;
>   	mutex_unlock(&device->dev_set->lock);
>   
>   	module_put(device->dev->driver->owner);
> @@ -1726,8 +1745,8 @@ EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
>    * @file: VFIO group file
>    * @kvm: KVM to link
>    *
> - * The kvm pointer will be forwarded to all the vfio_device's attached to the
> - * VFIO file via the VFIO_GROUP_NOTIFY_SET_KVM notifier.
> + * When a VFIO device is first opened the KVM will be available in
> + * device->kvm if one was associated with the group.
>    */
>   void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
>   {
> @@ -1738,8 +1757,6 @@ void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
>   
>   	down_write(&group->group_rwsem);
>   	group->kvm = kvm;
> -	blocking_notifier_call_chain(&group->notifier,
> -				     VFIO_GROUP_NOTIFY_SET_KVM, kvm);
>   	up_write(&group->group_rwsem);
>   }
>   EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
> @@ -2006,7 +2023,8 @@ static int vfio_register_iommu_notifier(struct vfio_group *group,
>   	struct vfio_iommu_driver *driver;
>   	int ret;
>   
> -	down_read(&group->group_rwsem);
> +	lockdep_assert_held_read(&group->group_rwsem);
> +
>   	container = group->container;
>   	driver = container->iommu_driver;
>   	if (likely(driver && driver->ops->register_notifier))
> @@ -2014,7 +2032,6 @@ static int vfio_register_iommu_notifier(struct vfio_group *group,
>   						     events, nb);
>   	else
>   		ret = -ENOTTY;
> -	up_read(&group->group_rwsem);
>   
>   	return ret;
>   }
> @@ -2026,7 +2043,8 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
>   	struct vfio_iommu_driver *driver;
>   	int ret;
>   
> -	down_read(&group->group_rwsem);
> +	lockdep_assert_held_read(&group->group_rwsem);
> +
>   	container = group->container;
>   	driver = container->iommu_driver;
>   	if (likely(driver && driver->ops->unregister_notifier))
> @@ -2034,47 +2052,10 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
>   						       nb);
>   	else
>   		ret = -ENOTTY;
> -	up_read(&group->group_rwsem);
>   
>   	return ret;
>   }
>   
> -static int vfio_register_group_notifier(struct vfio_group *group,
> -					unsigned long *events,
> -					struct notifier_block *nb)
> -{
> -	int ret;
> -	bool set_kvm = false;
> -
> -	if (*events & VFIO_GROUP_NOTIFY_SET_KVM)
> -		set_kvm = true;
> -
> -	/* clear known events */
> -	*events &= ~VFIO_GROUP_NOTIFY_SET_KVM;
> -
> -	/* refuse to continue if still events remaining */
> -	if (*events)
> -		return -EINVAL;
> -
> -	ret = blocking_notifier_chain_register(&group->notifier, nb);
> -	if (ret)
> -		return ret;
> -
> -	/*
> -	 * The attaching of kvm and vfio_group might already happen, so
> -	 * here we replay once upon registration.
> -	 */
> -	if (set_kvm) {
> -		down_read(&group->group_rwsem);
> -		if (group->kvm)
> -			blocking_notifier_call_chain(&group->notifier,
> -						     VFIO_GROUP_NOTIFY_SET_KVM,
> -						     group->kvm);
> -		up_read(&group->group_rwsem);
> -	}
> -	return 0;
> -}
> -
>   int vfio_register_notifier(struct vfio_device *device,
>   			   enum vfio_notify_type type, unsigned long *events,
>   			   struct notifier_block *nb)
> @@ -2090,9 +2071,6 @@ int vfio_register_notifier(struct vfio_device *device,
>   	case VFIO_IOMMU_NOTIFY:
>   		ret = vfio_register_iommu_notifier(group, events, nb);
>   		break;
> -	case VFIO_GROUP_NOTIFY:
> -		ret = vfio_register_group_notifier(group, events, nb);
> -		break;
>   	default:
>   		ret = -EINVAL;
>   	}
> @@ -2114,9 +2092,6 @@ int vfio_unregister_notifier(struct vfio_device *device,
>   	case VFIO_IOMMU_NOTIFY:
>   		ret = vfio_unregister_iommu_notifier(group, nb);
>   		break;
> -	case VFIO_GROUP_NOTIFY:
> -		ret = blocking_notifier_chain_unregister(&group->notifier, nb);
> -		break;
>   	default:
>   		ret = -EINVAL;
>   	}
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 45b287826ce6..aa888cc51757 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -36,6 +36,8 @@ struct vfio_device {
>   	struct vfio_device_set *dev_set;
>   	struct list_head dev_set_list;
>   	unsigned int migration_flags;
> +	/* Driver must reference the kvm during open_device or never touch it */
> +	struct kvm *kvm;
>   
>   	/* Members below here are private, not for driver use */
>   	refcount_t refcount;
> @@ -155,15 +157,11 @@ extern int vfio_dma_rw(struct vfio_device *device, dma_addr_t user_iova,
>   /* each type has independent events */
>   enum vfio_notify_type {
>   	VFIO_IOMMU_NOTIFY = 0,
> -	VFIO_GROUP_NOTIFY = 1,
>   };
>   
>   /* events for VFIO_IOMMU_NOTIFY */
>   #define VFIO_IOMMU_NOTIFY_DMA_UNMAP	BIT(0)
>   
> -/* events for VFIO_GROUP_NOTIFY */
> -#define VFIO_GROUP_NOTIFY_SET_KVM	BIT(0)
> -
>   extern int vfio_register_notifier(struct vfio_device *device,
>   				  enum vfio_notify_type type,
>   				  unsigned long *required_events,