Hi Tomasz, On Mon, Mar 23, 2015 at 05:38:45PM +0900, Tomasz Figa wrote: > While unmapping, the driver zaps all iovas belonging to the mapping, > so the page tables not used by any mapping won't be cached. Now when > the driver creates a mapping it might end up occupying several page > tables. However, since the mapping area is virtually contiguous, only > the first and last page table can be shared with different mappings. > This means that only first and last iovas can be already cached. In > fact, we could detect if first and last page tables are shared and do > not zap at all, but this wouldn't really optimize too much. Why > invalidating one iova is enough to invalidate the whole page table is > unclear to me as well, but it seems to be the correct way on this > hardware. > > As for the race, it's also kind of explained by the above. The already > running hardware can trigger page table look-ups in the IOMMU and so > caching of the page table between our zapping and updating its > contents. With this patch zapping is performed after updating the page > table so the race is gone. Okay, this makes sense. Can you add this information to the patch changelog and resend please? Thanks, Joerg
