On Thu, Aug 13, 2015 at 7:31 AM, Christoph Hellwig <hch@xxxxxx> wrote: > On Wed, Aug 12, 2015 at 09:01:02AM -0700, Linus Torvalds wrote: >> I'm assuming that anybody who wants to use the page-less >> scatter-gather lists always does so on memory that isn't actually >> virtually mapped at all, or only does so on sane architectures that >> are cache coherent at a physical level, but I'd like that assumption >> *documented* somewhere. > > It's temporarily mapped by kmap-like helpers. That code isn't in > this series. The most recent version of it is here: > > https://git.kernel.org/cgit/linux/kernel/git/djbw/nvdimm.git/commit/?h=pfn&id=de8237c99fdb4352be2193f3a7610e902b9bb2f0 > > note that it's not doing the cache flushing it would have to do yet, but > it's also only enabled for x86 at the moment. For virtually tagged caches I assume we would temporarily map with kmap_atomic_pfn_t(), similar to how drm_clflush_pages() implements powerpc support. However with DAX we could end up with multiple virtual aliases for a page-less pfn.
