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

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Message-ID: <b7dd1cc5-849d-781e-ad08-c5b554900150@hisilicon.com>
Date: Wed, 6 Nov 2024 21:12:47 +0800
From: Junxian Huang <huangjunxian6@...ilicon.com>
To: Leon Romanovsky <leon@...nel.org>
CC: <dennis.dalessandro@...nelisnetworks.com>, <jgg@...pe.ca>,
	<linux-rdma@...r.kernel.org>, <linuxarm@...wei.com>,
	<linux-kernel@...r.kernel.org>, <tangchengchang@...wei.com>
Subject: Re: [PATCH for-next 0/2] Small optimization for ib_map_mr_sg() and
 ib_map_mr_sg_pi()



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.

Junxian

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