On Wed, 2013-09-25 at 17:54 +0200, Joerg Roedel wrote: > On Sat, Sep 21, 2013 at 09:59:00PM -0500, David Woodhouse wrote: > > I *hate* the bizarre calling convention for iommu_unmap(). Is it > > actually clearly documented anywhere? Why on earth is it not just > > returning void, and expected to unmap what it was *asked* to unmap? > > Yeah, I agree that this should be documented since it is quite > non-standard/non-obvious behaviour of a function. The reason the > interface was implemented this way is that the caller should not need to > know (or keep track of) the page-size which was used to map a given iova. > > So the interface is basically, that you give an iova and a size and the > iommu driver unmaps _at_least_ a region of that size. But if you ask for > a 4k region which is mapped by a 2M page then the whole 2M are unmapped. > The return value tells you how much was actually unmapped. > > Not the best interface, I know. We should come up with a better way to > handle this.
Actually, unmap can return zero too, which happens if you try to unmap an offset into a super page mapping. The current interface has issues, but both legacy kvm assignment and vfio rely on it so we don't need to track individual mappings. Thanks, Alex _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
