Linux Virtualization - Feb 2015 - [PATCH] virtio_pci: use 16-bit accessor for queue_enable.

Since PCI is little endian, 8-bit access might work, but the spec section
is very clear on this:

  4.1.3.1 Driver Requirements: PCI Device Layout

  The driver MUST access each field using the ?natural? access method,
  i.e. 32-bit accesses for 32-bit fields, 16-bit accesses for 16-bit
  fields and 8-bit accesses for 8-bit fields.

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff --git a/drivers/virtio/virtio_pci_modern.c
b/drivers/virtio/virtio_pci_modern.c
index f16e462cb4ef..2aa38e59db2e 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -294,7 +294,7 @@ static struct virtqueue *setup_vq(struct virtio_pci_device
*vp_dev,
 
 	/* Check if queue is either not available or already active. */
 	num = ioread16(&cfg->queue_size);
-	if (!num || ioread8(&cfg->queue_enable))
+	if (!num || ioread16(&cfg->queue_enable))
 		return ERR_PTR(-ENOENT);
 
 	if (num & (num - 1)) {
@@ -394,7 +394,7 @@ static int vp_modern_find_vqs(struct virtio_device *vdev,
unsigned nvqs,
 	 */
 	list_for_each_entry(vq, &vdev->vqs, list) {
 		iowrite16(vq->index, &vp_dev->common->queue_select);
-		iowrite8(1, &vp_dev->common->queue_enable);
+		iowrite16(1, &vp_dev->common->queue_enable);
 	}
 
 	return 0;

On Tue, Feb 10, 2015 at 05:05:01PM +1030, Rusty Russell
wrote:
> Since PCI is little endian, 8-bit access might work, but the spec section
> is very clear on this:
> 
>   4.1.3.1 Driver Requirements: PCI Device Layout
> 
>   The driver MUST access each field using the ?natural? access method,
>   i.e. 32-bit accesses for 32-bit fields, 16-bit accesses for 16-bit
>   fields and 8-bit accesses for 8-bit fields.
> 
> Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> diff --git a/drivers/virtio/virtio_pci_modern.c
b/drivers/virtio/virtio_pci_modern.c
> index f16e462cb4ef..2aa38e59db2e 100644
> --- a/drivers/virtio/virtio_pci_modern.c
> +++ b/drivers/virtio/virtio_pci_modern.c
> @@ -294,7 +294,7 @@ static struct virtqueue *setup_vq(struct
virtio_pci_device *vp_dev,
>  
>  	/* Check if queue is either not available or already active. */
>  	num = ioread16(&cfg->queue_size);
> -	if (!num || ioread8(&cfg->queue_enable))
> +	if (!num || ioread16(&cfg->queue_enable))
>  		return ERR_PTR(-ENOENT);
>  
>  	if (num & (num - 1)) {
> @@ -394,7 +394,7 @@ static int vp_modern_find_vqs(struct virtio_device
*vdev, unsigned nvqs,
>  	 */
>  	list_for_each_entry(vq, &vdev->vqs, list) {
>  		iowrite16(vq->index, &vp_dev->common->queue_select);
> -		iowrite8(1, &vp_dev->common->queue_enable);
> +		iowrite16(1, &vp_dev->common->queue_enable);
>  	}
>  
>  	return 0;