On Thu, Oct 29, 2015 at 09:42:12AM +0900, David Woodhouse wrote: > Aside from the lack of security, the other disadvantage of that is that > you have to pin *all* pages of a guest in case DMA happens; you don't > get to pin *only* those pages which are referenced by that guest's > IOMMU page tables... We do bypass the IOMMU but not the DMA API and given that before we call the DMA API we pin the page then we do not need to pin all the pages. Just the ones we use for the DMA. For me this flag looks orthogonal to the page pinning issue you brought. It is just a hint to the DMA API that we want to use simple & fast mapping while knowing we loose IOMMU protection for this memory. For the IB case, setting and tearing DMA mappings for the drivers data buffers is expensive. But we could for example consider to map all the HW control objects that validate the HW access to the drivers data buffers as IOMMU protected and so have IOMMU protection on those critical objects while having fast set-up/tear-down of driver data buffers. The HW control objects have stable mapping for the lifetime of the system. So the case of using both types of DMA mappings is still valid. > > -- > dwmw2 > > -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
