Re: [PATCH 2/3] virtio_ring: Support DMA APIs

From	Joerg Roedel <jroedel@suse.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/3] virtio_ring: Support DMA APIs
Date	2015-10-28 03:10 +0100
Message-ID	<qoolA-4PZ-1@gated-at.bofh.it> (permalink)
References	<qonzc-4kh-3@gated-at.bofh.it> <qonzc-4kh-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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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Thread

[PATCH 2/3] virtio_ring: Support DMA APIs Andy Lutomirski <luto@kernel.org> - 2015-10-28 02:20 +0100
  Re: [PATCH 2/3] virtio_ring: Support DMA APIs Joerg Roedel <jroedel@suse.de> - 2015-10-28 03:10 +0100
    Re: [PATCH 2/3] virtio_ring: Support DMA APIs Andy Lutomirski <luto@amacapital.net> - 2015-10-28 03:20 +0100
      Re: [PATCH 2/3] virtio_ring: Support DMA APIs Joerg Roedel <jroedel@suse.de> - 2015-10-28 03:30 +0100
        Re: [PATCH 2/3] virtio_ring: Support DMA APIs Andy Lutomirski <luto@amacapital.net> - 2015-10-28 06:20 +0100
  Re: [PATCH 2/3] virtio_ring: Support DMA APIs Christian Borntraeger <borntraeger@de.ibm.com> - 2015-10-28 03:30 +0100
    Re: [PATCH 2/3] virtio_ring: Support DMA APIs Andy Lutomirski <luto@amacapital.net> - 2015-10-28 06:10 +0100

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