On Wed, Aug 27, 2014 at 10:35:10AM -0700, Andy Lutomirski wrote:
> 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.
Right. It should fail back to 32-bit (the default on PCI bus).
I was merely thinking of the error reporting might be useful
but on second thought - saying that the user is screwed - is
a bad idea.
>
> If that's not a safe assumption, I can change it.
>
> --Andy
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