2015-02-10 06:41:59

by Rusty Russell

Subject: [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 <[email protected]>

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;

2015-02-10 06:57:54

by Michael S. Tsirkin

Subject: Re: [PATCH] virtio_pci: use 16-bit accessor for queue_enable.

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 <[email protected]>

Acked-by: Michael S. Tsirkin <[email protected]>

> 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;