Messages in this thread | | | From | Yongji Xie <> | Date | Wed, 6 Jul 2022 18:15:57 +0800 | Subject | Re: [PATCH v2 0/5] VDUSE: Support registering userspace memory as bounce buffer |
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On Wed, Jul 6, 2022 at 5:30 PM Jason Wang <jasowang@redhat.com> wrote: > > On Wed, Jul 6, 2022 at 1:05 PM Xie Yongji <xieyongji@bytedance.com> wrote: > > > > Hi all, > > > > This series introduces some new ioctls: VDUSE_IOTLB_GET_INFO, > > VDUSE_IOTLB_REG_UMEM and VDUSE_IOTLB_DEREG_UMEM to support > > registering and de-registering userspace memory for IOTLB > > as bounce buffer in virtio-vdpa case. > > > > The VDUSE_IOTLB_GET_INFO ioctl can help user to query IOLTB > > information such as bounce buffer size. Then user can use > > those information on VDUSE_IOTLB_REG_UMEM and > > VDUSE_IOTLB_DEREG_UMEM ioctls to register and de-register > > userspace memory for IOTLB. > > > > During registering and de-registering, the DMA data in use > > would be copied from kernel bounce pages to userspace bounce > > pages and back. > > > > With this feature, some existing application such as SPDK > > and DPDK can leverage the datapath of VDUSE directly and > > efficiently as discussed before [1][2]. They can register > > some preallocated hugepages to VDUSE to avoid an extra > > memcpy from bounce-buffer to hugepages. > > This is really interesting. > > But a small concern on uAPI is that this seems to expose the VDUSE > internal implementation (bounce buffer) to userspace. We tried hard to > hide it via the GET_FD before. Anyway can we keep it? >
Another way is changing GET_FD ioctl to add a flag or reuse 'perm' field to indicate whether a IOVA region supports userspace memory registration. Then userspace can use VDUSE_IOTLB_REG_UMEM/VDUSE_IOTLB_DEREG_UMEM to register/deregister userspace memory for this IOVA region. Any suggestions?
Thanks, Yongji
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