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From:   Christoph Hellwig <hch@lst.de>
To:     Linus Torvalds <torvalds@linux-foundation.org>
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Subject: Re: [PATCH 29/31] parisc: handle page-less SG entries
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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.