linux-kernel - Re: [PATCH] RDMA/mlx5: return the EFAULT per ibv_advise

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Date:   Sat, 21 Aug 2021 17:44:43 +0800
From:   "Li, Zhijian" <lizhijian@...fujitsu.com>
To:     Leon Romanovsky <leon@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        "Li Zhijian" <lizhijian@...fujitsu.com>
CC:     "dledford@...hat.com" <dledford@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RDMA/mlx5: return the EFAULT per ibv_advise_mr(3)

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Hi Jason & Leon

It reminds me that ibv_advise_mr doesn't mention ENOENT any more which value the API actually returns now.
the ENOENT cases/situations returned by kernel mlx5 implementation is most likely same with EINVALL as its manpage[1].

So shall we return EINVAL instead of ENOENT in kernel side when get_prefetchable_mr returns NULL?

1781 static int mlx5_ib_prefetch_sg_list(struct ib_pd *pd,
1782                     enum ib_uverbs_advise_mr_advice advice,
1783                     u32 pf_flags, struct ib_sge *sg_list,
1784                     u32 num_sge)
1785 {
1786     u32 bytes_mapped = 0;
1787     int ret = 0;
1788     u32 i;
1789
1790     for (i = 0; i < num_sge; ++i) {
1791         struct mlx5_ib_mr *mr;
1792
1793         mr = get_prefetchable_mr(pd, advice, sg_list[i].lkey);
1794         if (!mr)
1795             return -ENOENT;
1796         ret = pagefault_mr(mr, sg_list[i].addr, sg_list[i].length,
1797                    &bytes_mapped, pf_flags);



=============
RETURN VALUE
        ibv_advise_mr() returns 0 when the call was successful, or the value of errno on failure (which indicates the failure reason).

        EOPNOTSUPP
               libibverbs or provider driver doesn’t support the ibv_advise_mr() verb (ENOSYS may sometimes be returned by old versions of libibverbs).

        ENOTSUP
               The advise operation isn’t supported.

        EFAULT In  one of the following: o When the range requested is out of the MR bounds, or when parts of it are not part of the process address space.  o One of the lkeys provided in the scatter gather
               list is invalid or with wrong write access.

        EINVAL In one of the following: o The PD is invalid.  o The flags are invalid.

[1]:https://github.com/linux-rdma/rdma-core/blob/master/libibverbs/man/ibv_advise_mr.3.md

Thanks

on 2021/8/16 10:59, Li, Zhijian wrote:
> On 05/08/2021 14:43, Leon Romanovsky wrote:
>> On Wed, Aug 04, 2021 at 03:50:22PM -0300, Jason Gunthorpe wrote:
>>> On Wed, Aug 04, 2021 at 08:35:30AM +0300, Leon Romanovsky wrote:
>>>> On Tue, Aug 03, 2021 at 03:13:41PM -0300, Jason Gunthorpe wrote:
>>>>> On Tue, Aug 03, 2021 at 08:56:54PM +0300, Leon Romanovsky wrote:
>>>>>> On Tue, Aug 03, 2021 at 01:25:07PM -0300, Jason Gunthorpe wrote:
>>>>>>> On Sun, Aug 01, 2021 at 05:20:50PM +0800, Li Zhijian wrote:
>>>>>>>> ibv_advise_mr(3) says:
>>>>>>>> EFAULT In one of the following: o When the range requested is out of the  MR  bounds,
>>>>>>>>          or  when  parts of it are not part of the process address space. o One of the
>>>>>>>>          lkeys provided in the scatter gather list is invalid or with wrong write access
>>>>>>>>
>>>>>>>> Actually get_prefetchable_mr() will return NULL if it see above conditions
>>>>>>> No, get_prefetchable_mr() returns NULL if the mkey is invalid
>>>>>> And what is this?
>>>>>>     1701 static struct mlx5_ib_mr *
>>>>>>     1702 get_prefetchable_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
>>>>>>     1703                     u32 lkey)
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>     1721         /* prefetch with write-access must be supported by the MR */
>>>>>>     1722         if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
>>>>>>     1723             !mr->umem->writable) {
>>>>>>     1724                 mr = NULL;
>>>>>>     1725                 goto end;
>>>>>>     1726         }
>>>>> I would say that is an invalid mkey
>>>> I see it is as wrong write access.
>>> It just means the man page is wrong
>> ok, it can be a solution too.
> It sounds good.  I will try to update the manpage ibv_advise_mr(3) instead.
>
>
> Thanks
> Zhijian