Messages in this thread | | | Subject | Re: [ofa-general] iommu dma mapping alignment requirements | From | Tom Tucker <> | Date | Thu, 20 Dec 2007 11:29:36 -0600 |
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On Thu, 2007-12-20 at 11:14 -0600, Steve Wise wrote: > Hey Roland (and any iommu/ppc/dma experts out there): > > I'm debugging a data corruption issue that happens on PPC64 systems > running rdma on kernels where the iommu page size is 4KB yet the host > page size is 64KB. This "feature" was added to the PPC64 code recently, > and is in kernel.org from 2.6.23. So if the kernel is built with a 4KB > page size, no problems. If the kernel is prior to 2.6.23 then 64KB page > configs work too. Its just a problem when the iommu page size != host > page size. > > It appears that my problem boils down to a single host page of memory > that is mapped for dma, and the dma address returned by dma_map_sg() is > _not_ 64KB aligned. Here is an example: > > app registers va 0x000000002d9a3000 len 12288 > ib_umem_get() creates and maps a umem and chunk that looks like (dumping > state from a registered user memory region): > > > umem len 12288 off 12288 pgsz 65536 shift 16 > > chunk 0: nmap 1 nents 1 > > sglist[0] page 0xc000000000930b08 off 0 len 65536 dma_addr 000000005bff4000 dma_len 65536 > > > > So the kernel maps 1 full page for this MR. But note that the dma > address is 000000005bff4000 which is 4KB aligned, not 64KB aligned. I > think this is causing grief to the RDMA HW. > > My first question is: Is there an assumption or requirement in linux > that dma_addressess should have the same alignment as the host address > they are mapped to? IE the rdma core is mapping the entire 64KB page, > but the mapping doesn't begin on a 64KB page boundary. > > If this mapping is considered valid, then perhaps the rdma hw is at > fault here. But I'm wondering if this is an PPC/iommu bug. > > BTW: Here is what the Memory Region looks like to the HW: > > > TPT entry: stag idx 0x2e800 key 0xff state VAL type NSMR pdid 0x2 > > perms RW rem_inv_dis 0 addr_type VATO > > bind_enable 1 pg_size 65536 qpid 0x0 pbl_addr 0x003c67c0 > > len 12288 va 000000002d9a3000 bind_cnt 0 > > PBL: 000000005bff4000 > > > > Any thoughts?
The Ammasso certainly works this way. If you tell it the page size is 64KB, it will ignore bits in the page address that encode 0-65535.
> > Steve. > > > _______________________________________________ > general mailing list > general@lists.openfabrics.org > http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general > > To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
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