On Wed, Aug 27, 2014 at 10:32 AM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> On Tue, Aug 26, 2014 at 02:17:02PM -0700, Andy Lutomirski wrote:
>> A virtqueue is a coherent DMA mapping. Use the DMA API for it.
>> This fixes virtio_pci on Xen.
>>
>> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> ---
>> drivers/virtio/virtio_pci.c | 25 ++++++++++++++++++-------
>> 1 file changed, 18 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
>> index 3d1463c6b120..19039c5bec24 100644
>> --- a/drivers/virtio/virtio_pci.c
>> +++ b/drivers/virtio/virtio_pci.c
>> @@ -80,8 +80,9 @@ struct virtio_pci_vq_info
>> /* the number of entries in the queue */
>> int num;
>>
>> - /* the virtual address of the ring queue */
>> - void *queue;
>> + /* the ring queue */
>> + void *queue; /* virtual address */
>> + dma_addr_t queue_dma_addr; /* bus address */
>>
>> /* the list node for the virtqueues list */
>> struct list_head node;
>> @@ -417,15 +418,16 @@ static struct virtqueue *setup_vq(struct virtio_device *vdev, unsigned index,
>> info->num = num;
>> info->msix_vector = msix_vec;
>>
>> - size = PAGE_ALIGN(vring_size(num, VIRTIO_PCI_VRING_ALIGN));
>> - info->queue = alloc_pages_exact(size, GFP_KERNEL|__GFP_ZERO);
>> + size = vring_size(num, VIRTIO_PCI_VRING_ALIGN);
>> + info->queue = dma_zalloc_coherent(vdev->dev.parent, size,
>> + &info->queue_dma_addr, GFP_KERNEL);
>> if (info->queue == NULL) {
>> err = -ENOMEM;
>> goto out_info;
>> }
>>
>> /* activate the queue */
>> - iowrite32(virt_to_phys(info->queue) >> VIRTIO_PCI_QUEUE_ADDR_SHIFT,
>> + iowrite32(info->queue_dma_addr >> VIRTIO_PCI_QUEUE_ADDR_SHIFT,
>> vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
>>
>> /* create the vring */
>> @@ -462,7 +464,8 @@ out_assign:
>> vring_del_virtqueue(vq);
>> out_activate_queue:
>> iowrite32(0, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
>> - free_pages_exact(info->queue, size);
>> + dma_free_coherent(vdev->dev.parent, size,
>> + info->queue, info->queue_dma_addr);
>> out_info:
>> kfree(info);
>> return ERR_PTR(err);
>> @@ -493,7 +496,8 @@ static void vp_del_vq(struct virtqueue *vq)
>> iowrite32(0, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
>>
>> size = PAGE_ALIGN(vring_size(info->num, VIRTIO_PCI_VRING_ALIGN));
>> - free_pages_exact(info->queue, size);
>> + dma_free_coherent(vq->vdev->dev.parent, size,
>> + info->queue, info->queue_dma_addr);
>> kfree(info);
>> }
>>
>> @@ -712,6 +716,13 @@ static int virtio_pci_probe(struct pci_dev *pci_dev,
>> if (err)
>> goto out;
>>
>> + /*
>> + * We support 64-bit DMA. If this fails (e.g. some bridge
>> + * or PV code doesn't or DAC is disabled), then we're okay
>> + * with 32-bit DMA.
>
> <scratches his head>
>
> I am having a hard time parsing that. Could you expand a bit the
> faulting use-case please?
>
>> + */
>> + dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
>
> The usual process is:
>
> ret = dma_set_mask_and_coherent(..)
> if (ret)
> ret = dma_set_mask_and_coherent(.., DMA_BIT_MASK(32))
>
> if (ret)
> pr_warn("We are truly screwed. Good luck!\n");
>
I assumed that, if dma_set_mask_and_coherent(..., DMA_BIT_BASK(64))
fails, then we can still do DMA, just not 64-bit DMA. This driver
should be fine with that -- it'll just be a bit slower.
If that's not a safe assumption, I can change it.
--Andy
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