vfio: Add an option to get migration data size

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2158549
Conflicts: Partial, RHEL does not currently include hisi_acc or mlx5
           vfio-pci variant drivers.  Context, DMA dirty logging feature
           support via 80c4b92 ("vfio: Introduce the DMA logging
           feature support") not yet included.

commit 4e016f9
Author: Yishai Hadas <yishaih@nvidia.com>
Date:   Sun Nov 6 19:46:18 2022 +0200

    vfio: Add an option to get migration data size

    Add an option to get migration data size by introducing a new migration
    feature named VFIO_DEVICE_FEATURE_MIG_DATA_SIZE.

    Upon VFIO_DEVICE_FEATURE_GET the estimated data length that will be
    required to complete STOP_COPY is returned.

    This option may better enable user space to consider before moving to
    STOP_COPY whether it can meet the downtime SLA based on the returned
    data.

    The patch also includes the implementation for mlx5 and hisi for this
    new option to make it feature complete for the existing drivers in this
    area.

    Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
    Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
    Reviewed-by: Longfang Liu <liulongfang@huawei.com>
    Link: https://lore.kernel.org/r/20221106174630.25909-2-yishaih@nvidia.com
    Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: Alex Williamson

drivers/vfio/pci/vfio_pci_core.c

@@ -1865,7 +1865,8 @@ int vfio_pci_core_register_device(struct vfio_pci_core_device *vdev)
 
 	if (vdev->vdev.mig_ops) {
 		if (!(vdev->vdev.mig_ops->migration_get_state &&
-		      vdev->vdev.mig_ops->migration_set_state) ||
+		      vdev->vdev.mig_ops->migration_set_state &&
+		      vdev->vdev.mig_ops->migration_get_data_size) ||
 		    !(vdev->vdev.migration_flags & VFIO_MIGRATION_STOP_COPY))
 			return -EINVAL;
 	}

drivers/vfio/vfio_main.c

@@ -1630,6 +1630,34 @@ vfio_ioctl_device_feature_mig_device_state(struct vfio_device *device,
 	return 0;
 }
 
+static int
+vfio_ioctl_device_feature_migration_data_size(struct vfio_device *device,
+					      u32 flags, void __user *arg,
+					      size_t argsz)
+{
+	struct vfio_device_feature_mig_data_size data_size = {};
+	unsigned long stop_copy_length;
+	int ret;
+
+	if (!device->mig_ops)
+		return -ENOTTY;
+
+	ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET,
+				 sizeof(data_size));
+	if (ret != 1)
+		return ret;
+
+	ret = device->mig_ops->migration_get_data_size(device, &stop_copy_length);
+	if (ret)
+		return ret;
+
+	data_size.stop_copy_length = stop_copy_length;
+	if (copy_to_user(arg, &data_size, sizeof(data_size)))
+		return -EFAULT;
+
+	return 0;
+}
+
 static int vfio_ioctl_device_feature_migration(struct vfio_device *device,
 					       u32 flags, void __user *arg,
 					       size_t argsz)
@@ -1684,6 +1712,10 @@ static int vfio_ioctl_device_feature(struct vfio_device *device,
 		return vfio_ioctl_device_feature_mig_device_state(
 			device, feature.flags, arg->data,
 			feature.argsz - minsz);
+	case VFIO_DEVICE_FEATURE_MIG_DATA_SIZE:
+		return vfio_ioctl_device_feature_migration_data_size(
+			device, feature.flags, arg->data,
+			feature.argsz - minsz);
 	default:
 		if (unlikely(!device->ops->device_feature))
 			return -EINVAL;

include/linux/vfio.h

@@ -99,13 +99,18 @@ struct vfio_device_ops {
  * @migration_get_state: Optional callback to get the migration state for
  *         devices that support migration. It's mandatory for
  *         VFIO_DEVICE_FEATURE_MIGRATION migration support.
+ * @migration_get_data_size: Optional callback to get the estimated data
+ *          length that will be required to complete stop copy. It's mandatory for
+ *          VFIO_DEVICE_FEATURE_MIGRATION migration support.
  */
 struct vfio_migration_ops {
 	struct file *(*migration_set_state)(
 		struct vfio_device *device,
 		enum vfio_device_mig_state new_state);
 	int (*migration_get_state)(struct vfio_device *device,
 				   enum vfio_device_mig_state *curr_state);
+	int (*migration_get_data_size)(struct vfio_device *device,
+				       unsigned long *stop_copy_length);
 };
 
 /**

include/uapi/linux/vfio.h

@@ -986,6 +986,19 @@ enum vfio_device_mig_state {
 	VFIO_DEVICE_STATE_RUNNING_P2P = 5,
 };
 
+/*
+ * Upon VFIO_DEVICE_FEATURE_GET read back the estimated data length that will
+ * be required to complete stop copy.
+ *
+ * Note: Can be called on each device state.
+ */
+
+struct vfio_device_feature_mig_data_size {
+	__aligned_u64 stop_copy_length;
+};
+
+#define VFIO_DEVICE_FEATURE_MIG_DATA_SIZE 9
+
 /* -------- API for Type1 VFIO IOMMU -------- */
 
 /**