From: Joerg Roedel 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 Reviewed-by: Christoph Hellwig Signed-off-by: Joerg Roedel Signed-off-by: Michael S. Tsirkin --- 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)