linux-kernel - Re: [for-next PATCH 4/5] RDMA/rxe: refactor iova_to

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Date:   Fri, 18 Nov 2022 01:32:37 +0000
From:   "lizhijian@...itsu.com" <lizhijian@...itsu.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
CC:     Zhu Yanjun <zyjzyj2000@...il.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [for-next PATCH 4/5] RDMA/rxe: refactor iova_to_vaddr



On 16/11/2022 20:37, Fabio M. De Francesco wrote:
>> -     return (void *)(uintptr_t)mr->map[m]->buf[n].addr + offset;
>> +     if (mr->ibmr.type == IB_MR_TYPE_USER) {
>> +             char *paddr;
>> +             struct page *pg = mr->map[m]->buf[n].page;
>> +
>> +             paddr = kmap_local_page(pg);
>> +             if (paddr == NULL) {
>> +                     pr_warn("Failed to map page");
>> +                     return NULL;
>> +             }
> I know nothing about this code but I am here as a result of regular checks for
> changes to HIGHMEM mappings across the entire kernel. So please forgive me if
> I'm objecting to the correct changes.
> 
> 1) It looks like this code had a call to page_address() and you converted it
> to mapping with kmap_local_page().
> 
> If page_address() is related and it used to work properly, the page you are
> mapping cannot come from ZONE_HIGHMEM. 

Yes, you are totally right.


Therefore, kmap_local_page() looks like
> an overkill.


The confusion about the page_address() here has been raised for a long 
time[1][2].

https://www.spinics.net/lists/linux-rdma/msg113206.html
https://lore.kernel.org/all/20220121160654.GC773547@iweiny-DESK2.sc.intel.com/


Thanks
Zhijian

> 
> I'm probably missing something...
>