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

[Or Gerlitz]

Or Gerlitz wrote:
> 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.

Christoph, can you clarify this point?

Or.