linux-kernel - Re: [RFC PATCH rdma-next 05/10] RDMA/rxe: Allow registering persistent flag for pmem MR only

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Date:   Fri, 31 Dec 2021 03:34:49 +0000
From:   "lizhijian@...itsu.com" <lizhijian@...itsu.com>
To:     Tom Talpey <tom@...pey.com>,
        "lizhijian@...itsu.com" <lizhijian@...itsu.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "zyjzyj2000@...il.com" <zyjzyj2000@...il.com>,
        "jgg@...pe.ca" <jgg@...pe.ca>,
        "aharonl@...dia.com" <aharonl@...dia.com>,
        "leon@...nel.org" <leon@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mbloch@...dia.com" <mbloch@...dia.com>,
        "liweihang@...wei.com" <liweihang@...wei.com>,
        "liangwenpeng@...wei.com" <liangwenpeng@...wei.com>,
        "yangx.jy@...itsu.com" <yangx.jy@...itsu.com>,
        "rpearsonhpe@...il.com" <rpearsonhpe@...il.com>,
        "y-goto@...itsu.com" <y-goto@...itsu.com>
Subject: Re: [RFC PATCH rdma-next 05/10] RDMA/rxe: Allow registering
 persistent flag for pmem MR only


delete unreachable liweihang@...wei.com from recipients


On 31/12/2021 06:25, Tom Talpey wrote:
> On 12/28/2021 3:07 AM, Li Zhijian wrote:
>> Memory region should support 2 placement types: IB_ACCESS_FLUSH_PERSISTENT
>> and IB_ACCESS_FLUSH_GLOBAL_VISIBILITY, and only pmem/nvdimm has ability to
>> persist data(IB_ACCESS_FLUSH_PERSISTENT).
>>
>> Signed-off-by: Li Zhijian <lizhijian@...fujitsu.com>
>> ---
>>   drivers/infiniband/sw/rxe/rxe_mr.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/infiniband/sw/rxe/rxe_mr.c b/drivers/infiniband/sw/rxe/rxe_mr.c
>> index bcd5e7afa475..21616d058f29 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_mr.c
>> +++ b/drivers/infiniband/sw/rxe/rxe_mr.c
>> @@ -206,6 +206,11 @@ static bool iova_in_pmem(struct rxe_mr *mr, u64 iova, int length)
>>       return page_in_dev_pagemap(page);
>>   }
>>   +static bool ib_check_flush_access_flags(struct ib_mr *mr, u32 flags)
>> +{
>> +    return mr->is_pmem || !(flags & IB_ACCESS_FLUSH_PERSISTENT);
>> +}
>
> It is perfectly allowed to flush ordinary memory, persistence is
> another matter entirely. 
It did, but only allows for the MRs that registered FLUSH access flags.



> Is this subroutine checking for flush,
> or persistence? 

both, but it should be called in registering MR stage.
we have to 2 checking points, here is the 1st gate, where it prevent
local user from registering a persistent access flag to an ordinary memory.

2nd is in [RFC PATCH rdma-next 08/10] RDMA/rxe: Implement flush execution in responder side
where it prevent remote user to requesting persist data into an ordinary memory.

> Its name is confusing and needs to be clarified.

Err,  let me see.... a more suitable name is very welcome.


Thanks

>
>> +
>>   int rxe_mr_init_user(struct rxe_pd *pd, u64 start, u64 length, u64 iova,
>>                int access, struct rxe_mr *mr)
>>   {
>> @@ -282,6 +287,13 @@ int rxe_mr_init_user(struct rxe_pd *pd, u64 start, u64 length, u64 iova,
>>         // iova_in_pmem must be called after set is updated
>>       mr->ibmr.is_pmem = iova_in_pmem(mr, iova, length);
>> +    if (!ib_check_flush_access_flags(&mr->ibmr, access)) {
>> +        pr_err("Cannot set IB_ACCESS_FLUSH_PERSISTENT for non-pmem memory\n");
>> +        mr->state = RXE_MR_STATE_INVALID;
>> +        mr->umem = NULL;
>> +        err = -EINVAL;
>> +        goto err_release_umem;
>> +    }
>
> Setting is_pmem is reasonable, but again, this is confusing with respect
> to the region being flushable. In general, all memory is flushable,
> provided the platform supports any kind of cache flush (i.e. all of them).
>
> Tom.