Re: [Qemu-devel] [RFC v2 2/8] virtio: memory cache for packed ring

[Maxime Coquelin]

On 06/05/2018 09:07 PM, address@hidden wrote:
> From: Wei Xu <address@hidden>
>
> Mostly reuse memory cache with 1.0 except for the offset calculation.
>
> Signed-off-by: Wei Xu <address@hidden>
> ---
>   hw/virtio/virtio.c | 29 ++++++++++++++++++++---------
>   1 file changed, 20 insertions(+), 9 deletions(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index e192a9a..f6c0689 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -150,11 +150,8 @@ static void virtio_init_region_cache(VirtIODevice *vdev, 
> int n)
>       VRingMemoryRegionCaches *old = vq->vring.caches;
>       VRingMemoryRegionCaches *new;
>       hwaddr addr, size;
> -    int event_size;
>       int64_t len;
>   
> -    event_size = virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
> -
>       addr = vq->vring.desc;
>       if (!addr) {
>           return;
> @@ -168,7 +165,7 @@ static void virtio_init_region_cache(VirtIODevice *vdev, 
> int n)
>           goto err_desc;
>       }
>   

In the case of packed ring layout, the region's cache for the descs has
to be initialized as write-able, as the descriptors are written-back by
the device.

Following patch fixes the assert I'm facing, but we might want to
differentiate the split and packed cases as it is read-only in split
case:

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 012c0925f2..4b165aaf2c 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -173,7 +173,7 @@ static void virtio_init_region_cache(VirtIODevice 
*vdev, int n)
     new = g_new0(VRingMemoryRegionCaches, 1);
     size = virtio_queue_get_desc_size(vdev, n);
     len = address_space_cache_init(&new->desc, vdev->dma_as,
-                                   addr, size, false);
+                                   addr, size, true);
     if (len < size) {
         virtio_error(vdev, "Cannot map desc");
         goto err_desc;


> -    size = virtio_queue_get_used_size(vdev, n) + event_size;
> +    size = virtio_queue_get_used_size(vdev, n);
>       len = address_space_cache_init(&new->used, vdev->dma_as,
>                                      vq->vring.used, size, true);
>       if (len < size) {
> @@ -176,7 +173,7 @@ static void virtio_init_region_cache(VirtIODevice *vdev, 
> int n)
>           goto err_used;
>       }
>   
> -    size = virtio_queue_get_avail_size(vdev, n) + event_size;
> +    size = virtio_queue_get_avail_size(vdev, n);
>       len = address_space_cache_init(&new->avail, vdev->dma_as,
>                                      vq->vring.avail, size, false);
>       if (len < size) {
> @@ -2320,14 +2317,28 @@ hwaddr virtio_queue_get_desc_size(VirtIODevice *vdev, 
> int n)
>   
>   hwaddr virtio_queue_get_avail_size(VirtIODevice *vdev, int n)
>   {
> -    return offsetof(VRingAvail, ring) +
> -        sizeof(uint16_t) * vdev->vq[n].vring.num;
> +    int s;
> +
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        return sizeof(struct VRingPackedDescEvent);
> +    } else {
> +        s = virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
> +        return offsetof(VRingAvail, ring) +
> +            sizeof(uint16_t) * vdev->vq[n].vring.num + s;
> +    }
>   }
>   
>   hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n)
>   {
> -    return offsetof(VRingUsed, ring) +
> -        sizeof(VRingUsedElem) * vdev->vq[n].vring.num;
> +    int s;
> +
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
> +        return sizeof(struct VRingPackedDescEvent);
> +    } else {
> +        s = virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
> +        return offsetof(VRingUsed, ring) +
> +            sizeof(VRingUsedElem) * vdev->vq[n].vring.num + s;
> +    }
>   }
>   
>   uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n)