On Tue, Feb 26, 2019 at 12:24:08PM +0100, Stanislaw Gruszka wrote: > On Tue, Feb 26, 2019 at 11:44:13AM +0100, Joerg Roedel wrote: > > On Tue, Feb 26, 2019 at 11:34:51AM +0100, Stanislaw Gruszka wrote: > > > On Tue, Feb 26, 2019 at 11:05:36AM +0100, Joerg Roedel wrote: > > > If sg->offset > PAGE_SIZE is fine then most likely we have problem with > > > alignment. > > > > The map_sg implementation in the AMD IOMMU driver uses sg_phys() which > > handles the sg->page + sg->offset calculation fine. > > > > > Note hat issue is with dma_map_sg(), switching to dma_map_single() > > > by using urb->transfer_buffer instead of urb->sg make things work > > > on AMD IOMMU. > > > > On the other hand this points to a bug in the driver, I'll look further > > if I can spot something there. > > I think so too. And I have done some changes that avoid strange allocation > scheme and use usb synchronous messages instead of allocating buffers > with unaligned sizes. However things work ok on Intel IOMMU and > there is no documentation what are dma_map_sg() requirement versus > dma_map_single() which works. I think there are some unwritten > requirements and things can work on some platforms and fails on others > (different IOMMUs, no-IOMMU on some ARCHes) For the record: we have another bug report with this issue: https://bugzilla.kernel.org/show_bug.cgi?id=202673 I provided there patch that change alignment for page_frag_alloc() and it did not fixed the problem. So this is not alignment issue. Now I think it could be page->refcount issue ... Stanislaw
