linux-kernel - Re: [PATCH RFC 1/2] RDMA/rxe: don't allow registering !PAGE

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Message-ID: <80ea66c5-2afc-43c5-b1f5-66cc2e62295d@fujitsu.com>
Date:   Tue, 31 Oct 2023 09:59:54 +0000
From:   "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     "zyjzyj2000@...il.com" <zyjzyj2000@...il.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rpearsonhpe@...il.com" <rpearsonhpe@...il.com>,
        "Daisuke Matsuda (Fujitsu)" <matsuda-daisuke@...itsu.com>,
        "bvanassche@....org" <bvanassche@....org>
Subject: Re: [PATCH RFC 1/2] RDMA/rxe: don't allow registering !PAGE_SIZE mr



On 30/10/2023 20:40, Jason Gunthorpe wrote:
> On Mon, Oct 30, 2023 at 07:51:41AM +0000, Zhijian Li (Fujitsu) wrote:
>>
>>
>> On 27/10/2023 13:41, Li Zhijian wrote:
>>> mr->page_list only encodes *page without page offset, when
>>> page_size != PAGE_SIZE, we cannot restore the address with a wrong
>>> page_offset.
>>>
>>> Note that this patch will break some ULPs that try to register 4K
>>> MR when PAGE_SIZE is not 4K.
>>> SRP and nvme over RXE is known to be impacted.
>>>
>>> Signed-off-by: Li Zhijian <lizhijian@...itsu.com>
>>> ---
>>>    drivers/infiniband/sw/rxe/rxe_mr.c | 6 ++++++
>>>    1 file changed, 6 insertions(+)
>>>
>>> diff --git a/drivers/infiniband/sw/rxe/rxe_mr.c b/drivers/infiniband/sw/rxe/rxe_mr.c
>>> index f54042e9aeb2..61a136ea1d91 100644
>>> --- a/drivers/infiniband/sw/rxe/rxe_mr.c
>>> +++ b/drivers/infiniband/sw/rxe/rxe_mr.c
>>> @@ -234,6 +234,12 @@ int rxe_map_mr_sg(struct ib_mr *ibmr, struct scatterlist *sgl,
>>>    	struct rxe_mr *mr = to_rmr(ibmr);
>>>    	unsigned int page_size = mr_page_size(mr);
>>>    
>>> +	if (page_size != PAGE_SIZE) {
>>
>> It seems this condition is too strict, it should be:
>> 	if (!IS_ALIGNED(page_size, PAGE_SIZE))
>>

I have to say I retract this conclusion. It still misses something.

To support PAGE_SIZE aligned MR, we have to refactor rxe_map_mr_sg() or rxe_set_page()

Currently, rxe_set_page() will be called in the step of page_size, this doesn't split N*PAGE_SIZE memory into
N *page. So when we restore an iova from xarray, the array index is wrong as well.

So i'm going to refactor rxe_map_mr_sg() to iterate the sgl by myself in rxe_map_mr_sg() like SIW does.
Hope this refactor can help RXE to support SZ_4K when PAGE_SIZE!=4K as well.


Thanks
Zhijian


>> So that, page_size with (N * PAGE_SIZE) can work as previously.
>> Because the offset(mr.iova & page_mask) will get lost only when !IS_ALIGNED(page_size, PAGE_SIZE)
> 
> That makes sense
> 
> Jason