Re: [Qemu-devel] [PATCH v2 3/5] vhost-user: support registering external host notifiers

[Tiwei Bie]

On Fri, May 25, 2018 at 07:26:05PM +0800, Jason Wang wrote:
> On 2018年05月25日 19:04, Tiwei Bie wrote:
[...]
> > +static int vhost_user_slave_handle_vring_host_notifier(struct vhost_dev 
> > *dev,
> > +                                                       VhostUserVringArea 
> > *area,
> > +                                                       int fd)
> > +{
> > +    int queue_idx = area->u64 & VHOST_USER_VRING_IDX_MASK;
> > +    size_t page_size = qemu_real_host_page_size;
> > +    struct vhost_user *u = dev->opaque;
> > +    VhostUserState *user = u->user;
> > +    VirtIODevice *vdev = dev->vdev;
> > +    VhostUserHostNotifier *n;
> > +    int ret = 0;
> > +    void *addr;
> > +    char *name;
> > +
> > +    if (!virtio_has_feature(dev->protocol_features,
> > +                            VHOST_USER_PROTOCOL_F_HOST_NOTIFIER) ||
> > +        vdev == NULL || queue_idx >= virtio_get_num_queues(vdev)) {
> > +        ret = -1;
> > +        goto out;
> > +    }
> > +
> > +    n = &user->notifier[queue_idx];
> > +
> > +    if (n->addr) {
> > +        virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, false);
> > +        object_unparent(OBJECT(&n->mr));
> > +        munmap(n->addr, page_size);
> > +        n->addr = NULL;
> > +    }
> > +
> > +    if (area->u64 & VHOST_USER_VRING_NOFD_MASK) {
> > +        goto out;
> > +    }
> > +
> > +    /* Sanity check. */
> > +    if (area->size != page_size) {
> > +        ret = -1;
> > +        goto out;
> > +    }
> > +
> > +    addr = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED,
> 
> It looks to me that PROT_WRITE is sufficient here?
> 
> Thanks
> 

I think it's safer to add PROT_READ. And there's
no harm to do that.

Best regards,
Tiwei Bie