On Thu, Aug 13, 2015 at 7:31 AM, Christoph Hellwig <hch(a)lst.de> 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:
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.