linux-kernel - Re: [RFC PATCH rdma-next 08/10] RDMA/rxe: Implement flush execution in responder side

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Date:   Mon, 10 Jan 2022 05:45:47 +0000
From:   "lizhijian@...itsu.com" <lizhijian@...itsu.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "zyjzyj2000@...il.com" <zyjzyj2000@...il.com>,
        "aharonl@...dia.com" <aharonl@...dia.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mbloch@...dia.com" <mbloch@...dia.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 08/10] RDMA/rxe: Implement flush execution
 in responder side

Hi Jason


On 07/01/2022 01:33, Jason Gunthorpe wrote:
> On Thu, Jan 06, 2022 at 06:42:57AM +0000, lizhijian@...itsu.com wrote:
>>
>> On 06/01/2022 08:28, Jason Gunthorpe wrote:
>>> On Tue, Dec 28, 2021 at 04:07:15PM +0800, Li Zhijian wrote:
>>>> +	while (length > 0) {
>>>> +		va	= (u8 *)(uintptr_t)buf->addr + offset;
>>>> +		bytes	= buf->size - offset;
>>>> +
>>>> +		if (bytes > length)
>>>> +			bytes = length;
>>>> +
>>>> +		arch_wb_cache_pmem(va, bytes);
>>> So why did we need to check that the va was pmem to call this?
>> Sorry, i didn't get you.
>>
>> I didn't check whether va is pmem, since only MR registered with PERSISTENCE(only pmem can
>> register this access flag) can reach here.
> Yes, that is what I mean,

I'm not sure I understand the *check* you mentioned above.

Current code just dose something like:

if (!sanity_check())
     return;
if (requested_plt == PERSISTENCE)
     va = iova_to_va(iova);
     arch_wb_cache_pmem(va, bytes);
     wmb;
else if (requested_plt == GLOBAL_VISIBILITY)
     wmb();


> why did we need to check anything to call
> this API
As above pseudo code,  it didn't *check* anything as what you said i think.


> - it should work on any CPU mapped address.
Of course, arch_wb_cache_pmem(va, bytes) works on CPU mapped address backing to both dimm and nvdimm,
but not a iova that could refers to user space address.


Thanks
Zhijian



>
> Jason