Jason Wang
2021-Mar-05 06:51 UTC
[RFC v4 06/11] vduse: Implement an MMU-based IOMMU driver
On 2021/3/5 2:15 ??, Yongji Xie wrote:>>>> Sorry if I've asked this before. >>>> >>>> But what's the reason for maintaing a dedicated IOTLB here? I think we >>>> could reuse vduse_dev->iommu since the device can not be used by both >>>> virtio and vhost in the same time or use vduse_iova_domain->iotlb for >>>> set_map(). >>>> >>> The main difference between domain->iotlb and dev->iotlb is the way to >>> deal with bounce buffer. In the domain->iotlb case, bounce buffer >>> needs to be mapped each DMA transfer because we need to get the bounce >>> pages by an IOVA during DMA unmapping. In the dev->iotlb case, bounce >>> buffer only needs to be mapped once during initialization, which will >>> be used to tell userspace how to do mmap(). >>> >>>> Also, since vhost IOTLB support per mapping token (opauqe), can we use >>>> that instead of the bounce_pages *? >>>> >>> Sorry, I didn't get you here. Which value do you mean to store in the >>> opaque pointer? >> So I would like to have a way to use a single IOTLB for manage all kinds >> of mappings. Two possible ideas: >> >> 1) map bounce page one by one in vduse_dev_map_page(), in >> VDUSE_IOTLB_GET_FD, try to merge the result if we had the same fd. Then >> for bounce pages, userspace still only need to map it once and we can >> maintain the actual mapping by storing the page or pa in the opaque >> field of IOTLB entry. > Looks like userspace still needs to unmap the old region and map a new > region (size is changed) with the fd in each VDUSE_IOTLB_GET_FD ioctl.I don't get here. Can you give an example?> >> 2) map bounce page once in vduse_dev_map_page() and store struct page >> **bounce_pages in the opaque field of this single IOTLB entry. >> > We can get the struct page **bounce_pages from vduse_iova_domain. Why > do we need to store it in the opaque field? Should the opaque field > be used to store vdpa_map_file?Oh yes, you're right.> > And I think it works. One problem is we need to find a place to store > the original DMA buffer's address and size. I think we can modify the > array of bounce_pages for this purpose. > > Thanks, > YongjiYes. Thanks>-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20210305/2e90b30e/attachment-0001.html>