[openib-general] [PATCH 1/7] IB/core - Add DMA mapping functions to allow device drivers to interpose

[Or Gerlitz]

On 11/5/06, Roland Dreier <rdreier at cisco.com> wrote:
>  > I have mentioned this to Ralph in the past, just want to get ack/nak
>  > on that from you: also on 64bit arch a block driver (eg SCSI LLD eg
>  > SRP/iSER/etc) might get from higher level an SG whose pages are
>  > **not** mapped into the kernel virtual address space. For example this
>  > can happen with Direct I/O.
>
> No, I don't see how that could happen.  Aren't all pages always mapped
> by the the kernel direct mapping on 64-bit architectures?

I don't know exactly how this happens, but one of the comments i've
got from Christoph
on the iser code, is that one can't assume page_address(sg[i].page)
will not be NULL for SG passed to a SCSI LLD, i think Direct I/O is
one flow where this might happen.

Or.