Messages in this thread | | | Subject | Re: [PATCH RFC] uaccess: user_access_begin_after_access_ok() | From | Jason Wang <> | Date | Wed, 3 Jun 2020 14:23:08 +0800 |
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On 2020/6/3 下午1:46, Michael S. Tsirkin wrote: > On Wed, Jun 03, 2020 at 01:18:54PM +0800, Jason Wang wrote: >> On 2020/6/3 下午12:18, Al Viro wrote: >>> On Wed, Jun 03, 2020 at 11:57:11AM +0800, Jason Wang wrote: >>> >>>>> How widely do you hope to stretch the user_access areas, anyway? >>>> To have best performance for small packets like 64B, if possible, we want to >>>> disable STAC not only for the metadata access done by vhost accessors but >>>> also the data access via iov iterator. >>> If you want to try and convince Linus to go for that, make sure to Cc >>> me on that thread. Always liked quality flame... >>> >>> The same goes for interval tree lookups with uaccess allowed. IOW, I _really_ >>> doubt that it's a good idea. >> >> I see. We are just seeking an approach to perform better in order to compete >> with userspace dpdk backends. >> >> I tried another approach of using direct mapping + mmu notifier [1] but the >> synchronization with MMU notifier is not easy to perform well. >> >> [1] https://patchwork.kernel.org/patch/11133009/ >> >> >>>>> Incidentally, who had come up with the name __vhost_get_user? >>>>> Makes for lovey WTF moment for readers - esp. in vhost_put_user()... >>>> I think the confusion comes since it does not accept userspace pointer (when >>>> IOTLB is enabled). >>>> >>>> How about renaming it as vhost_read()/vhost_write() ? >>> Huh? >>> >>> __vhost_get_user() is IOTLB remapping of userland pointer. It does not access >>> userland memory. Neither for read, nor for write. It is used by vhost_get_user() >>> and vhost_put_user(). >>> >>> Why would you want to rename it into vhost_read _or_ vhost_write, and in any case, >>> how do you give one function two names? IDGI... >> >> I get you know, I thought you're concerning the names of >> vhost_get_user()/vhost_put_user() but actually __vhost_get_user(). >> >> Maybe something like __vhost_fetch_uaddr() is better. >> >> Thanks > > It's basically vhost_translate_uaddr isn't it?
Yes.
> > BTW now I re-read it I don't understand __vhost_get_user_slow: > > > static void __user *__vhost_get_user_slow(struct vhost_virtqueue *vq, > void __user *addr, unsigned int size, > int type) > { > int ret; > > ret = translate_desc(vq, (u64)(uintptr_t)addr, size, vq->iotlb_iov, > ARRAY_SIZE(vq->iotlb_iov), > VHOST_ACCESS_RO); > > .. > } > > how does this work? how can we cast a pointer to guest address without > adding any offsets?
I'm not sure I get you here. What kind of offset did you mean?
Thanks
> >
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