[PATCH 3/3] virtio_pci: Use the DMA API for virtqueues

Andy Lutomirski
Tue, 26 Aug 2014 21:17:02 -0000

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 at amacapital.net>
---
 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.
+	 */
+	dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
+
 	err = pci_request_regions(pci_dev, "virtio-pci");
 	if (err)
 		goto out_enable_device;
--
1.9.3