From: Joerg Roedel <jroedel@suse.de>
Date: Thu, 7 Feb 2019 12:59:16 +0100
Subject: virtio: Introduce virtio_max_dma_size()
Git-commit: e6d6dd6c875eb3c9b69bb640419405726e6e0bbe
Patch-mainline: v5.1-rc1
References: bsc#1120008

This function returns the maximum segment size for a single
dma transaction of a virtio device. The possible limit comes
from the SWIOTLB implementation in the Linux kernel, that
has an upper limit of (currently) 256kb of contiguous
memory it can map. Other DMA-API implementations might also
have limits.

Use the new dma_max_mapping_size() function to determine the
maximum mapping size when DMA-API is in use for virtio.

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/virtio/virtio_ring.c | 11 +++++++++++
 include/linux/virtio.h       |  2 ++
 2 files changed, 13 insertions(+)

--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1013,6 +1013,17 @@ struct virtqueue *__vring_new_virtqueue(
 }
 EXPORT_SYMBOL_GPL(__vring_new_virtqueue);
 
+size_t virtio_max_dma_size(struct virtio_device *vdev)
+{
+	size_t max_segment_size = SIZE_MAX;
+
+	if (vring_use_dma_api(vdev))
+		max_segment_size = dma_max_mapping_size(&vdev->dev);
+
+	return max_segment_size;
+}
+EXPORT_SYMBOL_GPL(virtio_max_dma_size);
+
 static void *vring_alloc_queue(struct virtio_device *vdev, size_t size,
 			      dma_addr_t *dma_handle, gfp_t flag)
 {
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -156,6 +156,8 @@ int virtio_device_freeze(struct virtio_d
 int virtio_device_restore(struct virtio_device *dev);
 #endif
 
+size_t virtio_max_dma_size(struct virtio_device *vdev);
+
 #define virtio_device_for_each_vq(vdev, vq) \
 	list_for_each_entry(vq, &vdev->vqs, list)