On Tue, Oct 03, 2017 at 07:05:17PM +0100, Robin Murphy wrote: > Now, there are indeed plenty of drivers and subsystems which do work on > lists of explicitly single pages - anything doing some variant of > "addr = kmap_atomic(sg_page(sg)) + sg->offset;" is easy to spot - but I > don't think DMA API implementations are in a position to make any kind > of assumption; nearly all of them just shut up and handle sg->length > bytes from sg_phys(sg) without questioning the caller, and I reckon > that's exactly what they should be doing. I agree with that, it is not explicitly forbidden to have an sg->offset > PAGE_SIZE and most IOMMU drivers handle this case. So this is a problem I'd like to see resolved in the VT-d driver too. If nobody comes up with a correct fix soon I'll apply this one and rip out the large-page support from __domain_mapping() to make it work. Speaking of __domain_mapping(), this function is a big unmaintainable mess which should be split and rewritten. A clean and maintainable rewrite can alse re-add the large-page support. Regards, Joerg
