Re: [PATCH 2/2] vhost-vdpa: doorbell mapping support

[Si-Wei Liu <si-wei.liu@oracle.com>]

On 4/15/2021 1:04 AM, Jason Wang wrote:
> This patch implements the doorbell mapping support for
> vhost-vDPA. This is simply done by using mmap()/munmap() for the
> vhost-vDPA fd during device start/stop. For the device without
> doorbell support, we fall back to eventfd based notification
> gracefully.
>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>   hw/virtio/vhost-vdpa.c         | 85 ++++++++++++++++++++++++++++++++++
>   include/hw/virtio/vhost-vdpa.h |  7 +++
>   2 files changed, 92 insertions(+)
>
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index dd4321bac2..c3a3b7566f 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -285,12 +285,95 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque)
>       return 0;
>   }
>   
> +static void vhost_vdpa_host_notifier_uninit(struct vhost_dev *dev,
> +                                            int queue_index)
> +{
> +    size_t page_size = qemu_real_host_page_size;
> +    struct vhost_vdpa *v = dev->opaque;
> +    VirtIODevice *vdev = dev->vdev;
> +    VhostVDPAHostNotifier *n;
> +
> +    n = &v->notifier[queue_index];
> +
> +    if (n->addr) {
> +        virtio_queue_set_host_notifier_mr(vdev, queue_index, &n->mr, false);
> +        object_unparent(OBJECT(&n->mr));
> +        munmap(n->addr, page_size);
> +        n->addr = NULL;
> +    }
> +}
> +
> +static void vhost_vdpa_host_notifiers_uninit(struct vhost_dev *dev, int n)
> +{
> +    int i;
> +
> +    for (i = 0; i < n; i++) {
> +        vhost_vdpa_host_notifier_uninit(dev, i);
> +    }
> +}
> +
> +static int vhost_vdpa_host_notifier_init(struct vhost_dev *dev, int queue_index)
> +{
> +    size_t page_size = qemu_real_host_page_size;
> +    struct vhost_vdpa *v = dev->opaque;
> +    VirtIODevice *vdev = dev->vdev;
> +    VhostVDPAHostNotifier *n;
> +    int fd = v->device_fd;
> +    void *addr;
> +    char *name;
> +
> +    vhost_vdpa_host_notifier_uninit(dev, queue_index);
> +
> +    n = &v->notifier[queue_index];
> +
> +    addr = mmap(NULL, page_size, PROT_WRITE, MAP_SHARED, fd,
> +                queue_index * page_size);
> +    if (addr == MAP_FAILED) {
> +        goto err;
> +    }
> +
> +    name = g_strdup_printf("vhost-vdpa/host-notifier@%p mmaps[%d]",
> +                           v, queue_index);
> +    memory_region_init_ram_device_ptr(&n->mr, OBJECT(vdev), name,
> +                                      page_size, addr);
> +    g_free(name);
> +
> +    if (virtio_queue_set_host_notifier_mr(vdev, queue_index, &n->mr, true)) {
> +        munmap(addr, page_size);
> +        goto err;
> +    }
> +    n->addr = addr;
> +
> +    return 0;
> +
> +err:
> +    return -1;
> +}
> +
> +static void vhost_vdpa_host_notifiers_init(struct vhost_dev *dev)
> +{
> +    int i;
> +
> +    for (i = 0; i < dev->nvqs; i++) {
> +        if (vhost_vdpa_host_notifier_init(dev, i)) {
Shouldn't (hdev->vq_index + i) be used instead of i? or it's assumed to 
be single QP for vhost-vdpa for the moment? If the latter, would be good 
to add some comment.
> +            goto err;
> +        }
> +    }
> +
> +    return;
> +
> +err:
> +    vhost_vdpa_host_notifiers_uninit(dev, i);
I'm not sure if it is really the intent to leave other vqs behind - I 
presume that either none of them is mapped, or all mappable should be 
mapped. Why here just uninit the first unmappable vq?

> +    return;
> +}
> +
>   static int vhost_vdpa_cleanup(struct vhost_dev *dev)
>   {
>       struct vhost_vdpa *v;
>       assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_VDPA);
>       v = dev->opaque;
>       trace_vhost_vdpa_cleanup(dev, v);
> +    vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
>       memory_listener_unregister(&v->listener);
>   
>       dev->opaque = NULL;
> @@ -467,6 +550,7 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
>       if (started) {
>           uint8_t status = 0;
>           memory_listener_register(&v->listener, &address_space_memory);
> +        vhost_vdpa_host_notifiers_init(dev);
>           vhost_vdpa_set_vring_ready(dev);
>           vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
>           vhost_vdpa_call(dev, VHOST_VDPA_GET_STATUS, &status);
> @@ -476,6 +560,7 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
>           vhost_vdpa_reset_device(dev);
>           vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
>                                      VIRTIO_CONFIG_S_DRIVER);
> +        vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
>           memory_listener_unregister(&v->listener);
>   
>           return 0;
> diff --git a/include/hw/virtio/vhost-vdpa.h b/include/hw/virtio/vhost-vdpa.h
> index 9b81a409da..0f11ecff34 100644
> --- a/include/hw/virtio/vhost-vdpa.h
> +++ b/include/hw/virtio/vhost-vdpa.h
> @@ -14,11 +14,18 @@
>   
>   #include "hw/virtio/virtio.h"
>   
> +typedef struct VhostVDPAHostNotifier {
> +    MemoryRegion mr;
> +    void *addr;
> +} VhostVDPAHostNotifier;
> +
>   typedef struct vhost_vdpa {
>       int device_fd;
>       uint32_t msg_type;
>       MemoryListener listener;
>       struct vhost_dev *dev;
> +    VhostVDPAHostNotifier notifier[VIRTIO_QUEUE_MAX];
> +    bool host_notifier_set;
What this host_notifier_set is used for? Doesn't seem it's ever set or 
referenced?

>   } VhostVDPA;
>   
>   extern AddressSpace address_space_memory;
Thanks,
-Siwei