Re: [PATCH v3] IB/isert: fix unaligned immediate-data handling

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Sep 04, 2020 at 12:50:39PM -0700, Sagi Grimberg wrote:
> Currently we allocate rx buffers in a single contiguous buffers for
> headers (iser and iscsi) and data trailer. This means that most likely
> the data starting offset is aligned to 76 bytes (size of both headers).
> 
> This worked fine for years, but at some point this broke, resulting in
> data corruptions in isert when a command comes with immediate data
> and the underlying backend device assumes 512 bytes buffer alignment.
> 
> We assume a hard-requirement for all direct I/O buffers to be 512 bytes
> aligned. To fix this, we should avoid passing unaligned buffers for I/O.
> 
> Instead, we allocate our recv buffers with some extra space such that we
> can have the data portion align to 512 byte boundary. This also means
> that we cannot reference headers or data using structure but rather
> accessors (as they may move based on alignment). Also, get rid of the
> wrong __packed annotation from iser_rx_desc as this has only harmful
> effects (not aligned to anything).
> 
> This affects the rx descriptors for iscsi login and data plane.
> 
> Fixes: 3d75ca0adef4 ("block: introduce multi-page bvec helpers")
> Reported-by: Stephen Rust <srust@blockbridge.com>
> Tested-by: Doug Dumitru <doug@dumitru.com>
> Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
> ---
> Changes from v2:
> - fixed 2 redundant newlines 
> - added fixes tag
> Changes from v1:
> - revised change log 

Applied to for-rc, thanks

Jason