On Tue, Jun 02, 2020 at 04:45:05AM -0400, Michael S. Tsirkin wrote: > So vhost needs to poke at userspace *a lot* in a quick succession. It > is thus benefitial to enable userspace access, do our thing, then > disable. Except access_ok has already been pre-validated with all the > relevant nospec checks, so we don't need that. Add an API to allow > userspace access after access_ok and barrier_nospec are done.
BTW, what are you going to do about vq->iotlb != NULL case? Because you sure as hell do *NOT* want e.g. translate_desc() under STAC. Disable it around the calls of translate_desc()? How widely do you hope to stretch the user_access areas, anyway? BTW, speaking of possible annotations: looks like there's a large subset of call graph that can be reached only from vhost_worker() or from several ioctls, with all uaccess limited to that subgraph (thankfully). Having that explicitly marked might be a good idea... Unrelated question, while we are at it: is there any point having vhost_get_user() a polymorphic macro? In all callers the third argument is __virtio16 __user * and the second one is an explicit *<something> where <something> is __virtio16 *. Similar for vhost_put_user(): in all callers the third arugment is __virtio16 __user * and the second - cpu_to_vhost16(vq, something). Incidentally, who had come up with the name __vhost_get_user? Makes for lovey WTF moment for readers - esp. in vhost_put_user()...