vfio/mdev: Pass in a struct vfio_device * to vfio_dma_rw()

Every caller has a readily available vfio_device pointer, use that instead
of passing in a generic struct device. Change vfio_dma_rw() to take in the
struct vfio_device and move the container users that would have been held
by vfio_group_get_external_user_from_dev() to vfio_dma_rw() directly, like
vfio_pin/unpin_pages().

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/4-v4-8045e76bf00b+13d-vfio_mdev_no_group_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/gpu/drm/i915/gvt/gvt.h

@@ -732,7 +732,7 @@ static inline int intel_gvt_read_gpa(struct intel_vgpu *vgpu, unsigned long gpa,
 {
 	if (!vgpu->attached)
 		return -ESRCH;
-	return vfio_dma_rw(vgpu->vfio_group, gpa, buf, len, false);
+	return vfio_dma_rw(&vgpu->vfio_device, gpa, buf, len, false);
 }
 
 /**
@@ -750,7 +750,7 @@ static inline int intel_gvt_write_gpa(struct intel_vgpu *vgpu,
 {
 	if (!vgpu->attached)
 		return -ESRCH;
-	return vfio_dma_rw(vgpu->vfio_group, gpa, buf, len, true);
+	return vfio_dma_rw(&vgpu->vfio_device, gpa, buf, len, true);
 }
 
 void intel_gvt_debugfs_remove_vgpu(struct intel_vgpu *vgpu);

drivers/vfio/vfio.c

@@ -2323,32 +2323,28 @@ EXPORT_SYMBOL(vfio_group_unpin_pages);
  * As the read/write of user space memory is conducted via the CPUs and is
  * not a real device DMA, it is not necessary to pin the user space memory.
  *
- * The caller needs to call vfio_group_get_external_user() or
- * vfio_group_get_external_user_from_dev() prior to calling this interface,
- * so as to prevent the VFIO group from disposal in the middle of the call.
- * But it can keep the reference to the VFIO group for several calls into
- * this interface.
- * After finishing using of the VFIO group, the caller needs to release the
- * VFIO group by calling vfio_group_put_external_user().
- *
- * @group [in]		: VFIO group
+ * @device [in]		: VFIO device
  * @user_iova [in]	: base IOVA of a user space buffer
  * @data [in]		: pointer to kernel buffer
  * @len [in]		: kernel buffer length
  * @write		: indicate read or write
  * Return error code on failure or 0 on success.
  */
-int vfio_dma_rw(struct vfio_group *group, dma_addr_t user_iova,
-		void *data, size_t len, bool write)
+int vfio_dma_rw(struct vfio_device *device, dma_addr_t user_iova, void *data,
+		size_t len, bool write)
 {
 	struct vfio_container *container;
 	struct vfio_iommu_driver *driver;
 	int ret = 0;
 
-	if (!group || !data || len <= 0)
+	if (!data || len <= 0)
 		return -EINVAL;
 
-	container = group->container;
+	ret = vfio_group_add_container_user(device->group);
+	if (ret)
+		return ret;
+
+	container = device->group->container;
 	driver = container->iommu_driver;
 
 	if (likely(driver && driver->ops->dma_rw))
@@ -2357,6 +2353,8 @@ int vfio_dma_rw(struct vfio_group *group, dma_addr_t user_iova,
 	else
 		ret = -ENOTTY;
 
+	vfio_group_try_dissolve_container(device->group);
+
 	return ret;
 }
 EXPORT_SYMBOL(vfio_dma_rw);

include/linux/vfio.h

@@ -161,7 +161,7 @@ extern int vfio_group_pin_pages(struct vfio_group *group,
 extern int vfio_group_unpin_pages(struct vfio_group *group,
 				  unsigned long *user_iova_pfn, int npage);
 
-extern int vfio_dma_rw(struct vfio_group *group, dma_addr_t user_iova,
+extern int vfio_dma_rw(struct vfio_device *device, dma_addr_t user_iova,
 		       void *data, size_t len, bool write);
 
 extern struct iommu_domain *vfio_group_iommu_domain(struct vfio_group *group);