Re: [PATCH for-next 0/2] Small optimization for ib_map_mr_sg() and ib_map_mr_sg_pi()

[Leon Romanovsky <leon@kernel.org>]

On Wed, Nov 06, 2024 at 09:12:47PM +0800, Junxian Huang wrote:
> 
> 
> On 2024/11/6 20:08, Leon Romanovsky wrote:
> > On Tue, Nov 05, 2024 at 08:08:39PM +0800, Junxian Huang wrote:
> >> ib_map_mr_sg() and ib_map_mr_sg_pi() allow ULPs to specify NULL as
> >> the sg_offset/data_sg_offset/meta_sg_offset arguments. Drivers who
> >> need to derefernce these arguments have to add NULL pointer checks
> >> to avoid crashing the kernel.
> >>
> >> This can be optimized by adding dummy sg_offset pointer to these
> >> two APIs. When the sg_offset arguments are NULL, pass the pointer
> >> of dummy to drivers. Drivers can always get a valid pointer, so no
> >> need to add NULL pointer checks.
> >>
> >> Junxian Huang (2):
> >>   RDMA/core: Add dummy sg_offset pointer for ib_map_mr_sg() and
> >>     ib_map_mr_sg_pi()
> >>   RDMA: Delete NULL pointer checks for sg_offset in .map_mr_sg ops
> >>
> >>  drivers/infiniband/core/verbs.c         | 12 +++++++++---
> >>  drivers/infiniband/hw/mlx5/mr.c         | 18 ++++++------------
> >>  drivers/infiniband/sw/rdmavt/trace_mr.h |  2 +-
> >>  3 files changed, 16 insertions(+), 16 deletions(-)
> > 
> > So what does this change give us?
> > We have same functionality, same number of lines, same everything ...
> > 
> 
> Actually this is inspired by an hns bug. When ib_map_mr_sg() passes a NULL
> sg_offset pointer to hns_roce_map_mr_sg(), we dereference this pointer
> without a NULL check.
> 
> Of course we can fix it by adding NULL check in hns, but I think this
> patch may be a better solution since the sg_offset is guaranteed to be
> a valid pointer. This could benefit future drivers who also want to
> dereference sg_offset, they won't need to care about NULL checks.

Let's fix hns please. We are moving away from SG in RDMA.

> 
> Junxian
> 
> > Thanks
> > 
> >>
> >> --
> >> 2.33.0
> >>
> >>