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: <c9aaf37b-c6d8-0609-0113-449a635ddfc2@hisilicon.com>
Date: Thu, 7 Nov 2024 09:41:54 +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 21:36, Leon Romanovsky wrote:
> 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.
> 

Sure, thanks

Junxian

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