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SubjectRe: [PATCH 2/3] virtio_ring: Support DMA APIs
Hi Andy,

On Tue, Oct 27, 2015 at 06:17:09PM -0700, Andy Lutomirski wrote:
> From: Andy Lutomirski <luto@amacapital.net>
>
> virtio_ring currently sends the device (usually a hypervisor)
> physical addresses of its I/O buffers. This is okay when DMA
> addresses and physical addresses are the same thing, but this isn't
> always the case. For example, this never works on Xen guests, and
> it is likely to fail if a physical "virtio" device ever ends up
> behind an IOMMU or swiotlb.

The overall code looks good, but I havn't seen and dma_sync* calls.
When swiotlb=force is in use this would break.

> + vq->vring.desc[head].addr = cpu_to_virtio64(_vq->vdev, vring_map_single(
> + vq,
> + desc, total_sg * sizeof(struct vring_desc),
> + DMA_TO_DEVICE));

Nit: I think readability could be improved here by using a temporary
variable for the return value of vring_map_single().


Joerg



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