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

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Date:   Fri, 27 Oct 2023 16:17:42 +0800
From:   Zhu Yanjun <yanjun.zhu@...ux.dev>
To:     Li Zhijian <lizhijian@...itsu.com>, zyjzyj2000@...il.com,
        jgg@...pe.ca, leon@...nel.org, linux-rdma@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rpearsonhpe@...il.com,
        matsuda-daisuke@...itsu.com, bvanassche@....org
Subject: Re: [PATCH RFC 1/2] RDMA/rxe: don't allow registering !PAGE_SIZE mr

在 2023/10/27 13:41, Li Zhijian 写道:
> 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.

When ULP uses folio or compound page, ULP can not work well with RXE 
after this commit is applied.

Perhaps removing page_size set in RXE is a good solution because 
page_size is set twice, firstly page_size is set in infiniband/core, 
secondly it is set in RXE.

When folio or compound page is used in ULP, it is very possible that 
page_size in infiniband/core is different from the page_size in RXE.

Not sure what problem this difference will cause.

Zhu Yanjun

> 
> 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) {
> +		rxe_info_mr(mr, "Unsupported MR with page_size %u, expect %lu\n",
> +			   page_size, PAGE_SIZE);
> +		return -EOPNOTSUPP;
> +	}
> +
>   	mr->nbuf = 0;
>   	mr->page_shift = ilog2(page_size);
>   	mr->page_mask = ~((u64)page_size - 1);