netdev - Re: [PATCH v2 net-next 1/6] ch_ktls: Use memcpy_from_page() instead of k[un]map

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Date:   Mon, 28 Nov 2022 12:22:40 -0800
From:   Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
To:     Ayush Sawal <ayush.sawal@...lsio.com>, <netdev@...r.kernel.org>
CC:     Ira Weiny <ira.weiny@...el.com>,
        "Fabio M . De Francesco" <fmdefrancesco@...il.com>
Subject: Re: [PATCH v2 net-next 1/6] ch_ktls: Use memcpy_from_page() instead
 of k[un]map_atomic()

On 11/24/2022 2:56 AM, Ayush Sawal wrote:
> 
> On 11/24/2022 2:22 AM, Anirudh Venkataramanan wrote:
>> kmap_atomic() is being deprecated in favor of kmap_local_page(). Replace
>> the map-memcpy-unmap usage pattern (done using k[un]map_atomic()) with
>> memcpy_from_page(), which internally uses kmap_local_page() and
>> kunmap_local(). This renders the variables 'data' and 'vaddr' 
>> unnecessary,
>> and so remove these too.
>>
>> Note that kmap_atomic() disables preemption and page-fault processing, 
>> but
>> kmap_local_page() doesn't. When converting uses of kmap_atomic(), one has
>> to check if the code being executed between the map/unmap implicitly
>> depends on page-faults and/or preemption being disabled. If yes, then 
>> code
>> to disable page-faults and/or preemption should also be added for
>> functional correctness. That however doesn't appear to be the case here,
>> so just memcpy_from_page() is used.
>>
>> Also note that the page being mapped is not allocated by the driver, 
>> and so
>> the driver doesn't know if the page is in normal memory. This is the 
>> reason
>> kmap_local_page() is used (via memcpy_from_page()) as opposed to
>> page_address().
>>
>> I don't have hardware, so this change has only been compile tested.
>>
>> Cc: Ayush Sawal <ayush.sawal@...lsio.com>
>> Cc: Ira Weiny <ira.weiny@...el.com>
>> Cc: Fabio M. De Francesco <fmdefrancesco@...il.com>
>> Suggested-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
>> Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
>> ---
>> v1 -> v2:
>>   Use memcpy_from_page() as suggested by Fabio
>>   Add a "Suggested-by" tag
>>   Rework commit message
>>   Some emails cc'd in v1 are defunct. Drop them. The MAINTAINERS file for
>>   Chelsio drivers likely needs an update
>> ---
> 
> 
> Thanks for the patch.
> 
> Acked-by: Ayush Sawal <ayush.sawal@...lsio.com>

Thanks Ayush.

Please update the maintainers file for Chelsio drivers?

Ani