On 12/1/22 09:16, Bob Pearson wrote: > On 12/1/22 09:04, Bob Pearson wrote: >> On 11/30/22 18:41, Jason Gunthorpe wrote: >>> On Wed, Nov 30, 2022 at 06:36:56PM -0600, Bob Pearson wrote: >>>> I'm not looking at my patch you responded to but the one you posted to replace maps >>>> by xarrays. >>> >>> I see, I botched that part >>> >>>> The existing rxe driver assumes that if ibmr->type == IB_MR_TYPE_DMA >>>> that the iova is just a kernel (virtual) address that is already >>>> mapped. >>> >>> No, it is not correct >>> >>>> Maybe this is not correct but it has always worked this way. These >>>> are heavily used by storage stacks (e.g. Lustre) which always use >>>> DMA mr's. Since we don't actually do any DMAs we don't need to setup >>>> the iommu for these and just do memcpy's without dealing with pages. >>> >>> You still should be doing the kmap >>> >>> Jason >> >> Something was disconnected in my memory. So I went back and looked at lustre. >> Turns out it never uses IB_MR_TYPE_DMA and for that matter I can't find any >> use cases in the rdma tree or online. So, the implementation in rxe has almost >> certainly never been used. >> >> So I need to choose to 'fix' the current implementation or just delete type dma support. >> I get the idea that I need to convert the iova to a page and kmap it but i'm not >> clear how to do that. This 64 bit numnber (iova) needs to convert to a struct page *. >> Without a use case to look at I don't know how to interpret it. Apparently it's not a >> virtual address. >> >> Bob >> > > I did find a single use case for the mr created during alloc_pd. The comments seem > to imply that the use is just access to local kernel memory with va=pa. So I am back > to my previous thoughts. Memcpy should just work. > > Bob Further, looking at ipoib as an example, it builds sge lists using the lkey from get_dma_mr() and sets the sge->addr to a kernel virtual memory address after previously calling ib_dma_map_single() so the addresses are mapped for dma access and visible before use. They are unmapped after the read/write operation completes. What is the point of kmapping the address after dma mapping them? Bob
