netdev - Re: [PATCH net-next 1/5] ch_ktls: Use kmap_local_page() instead of kmap

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Date:   Fri, 18 Nov 2022 12:38:46 -0800
From:   Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        <netdev@...r.kernel.org>
CC:     Ira Weiny <ira.weiny@...el.com>,
        Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>
Subject: Re: [PATCH net-next 1/5] ch_ktls: Use kmap_local_page() instead of
 kmap_atomic()

On 11/18/2022 12:18 PM, Fabio M. De Francesco wrote:
> On venerdì 18 novembre 2022 19:27:56 CET Anirudh Venkataramanan wrote:
>> On 11/18/2022 12:14 AM, Fabio M. De Francesco wrote:
>>> On giovedì 17 novembre 2022 23:25:53 CET Anirudh Venkataramanan wrote:
>>>> kmap_atomic() is being deprecated in favor of kmap_local_page().
>>>> Replace kmap_atomic() and kunmap_atomic() with kmap_local_page()
>>>> and kunmap_local() respectively.
>>>>
>>>> Note that kmap_atomic() disables preemption and page-fault processing,
>>>> but kmap_local_page() doesn't. Converting the former to the latter is
> safe
>>>> only if there isn't an implicit dependency on preemption and page-fault
>>>> handling being disabled, which does appear to be the case here.
>>>>
>>>> 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 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: Vinay Kumar Yadav <vinay.yadav@...lsio.com>
>>>> Cc: Rohit Maheshwari <rohitm@...lsio.com>
>>>> Cc: Ira Weiny <ira.weiny@...el.com>
>>>> Cc: Fabio M. De Francesco <fmdefrancesco@...il.com>
>>>> Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
>>>> ---
>>>>
>>>>    .../ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c | 10 +++++-----
>>>>    1 file changed, 5 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/
> chcr_ktls.c
>>>> b/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c index
>>>> da9973b..d95f230 100644
>>>> --- a/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c
>>>> +++ b/drivers/net/ethernet/chelsio/inline_crypto/ch_ktls/chcr_ktls.c
>>>> @@ -1853,24 +1853,24 @@ static int chcr_short_record_handler(struct
>>>> chcr_ktls_info *tx_info, i++;
>>>>
>>>>    			}
>>>>    			f = &record->frags[i];
>>>>
>>>> -			vaddr = kmap_atomic(skb_frag_page(f));
>>>> +			vaddr = kmap_local_page(skb_frag_page(f));
>>>>
>>>>    			data = vaddr + skb_frag_off(f)  + remaining;
>>>>    			frag_delta = skb_frag_size(f) - remaining;
>>>>    			
>>>>    			if (frag_delta >= prior_data_len) {
>>>>    			
>>>>    				memcpy(prior_data, data,
>>>
>>> prior_data_len);
>>>
>>>> -				kunmap_atomic(vaddr);
>>>> +				kunmap_local(vaddr);
>>>>
>>>>    			} else {
>>>>    			
>>>>    				memcpy(prior_data, data, frag_delta);
>>>>
>>>> -				kunmap_atomic(vaddr);
>>>> +				kunmap_local(vaddr);
>>>>
>>>>    				/* get the next page */
>>>>    				f = &record->frags[i + 1];
>>>>
>>>> -				vaddr = kmap_atomic(skb_frag_page(f));
>>>> +				vaddr =
>>>
>>> kmap_local_page(skb_frag_page(f));
>>>
>>>>    				data = vaddr + skb_frag_off(f);
>>>>    				memcpy(prior_data + frag_delta,
>>>>    				
>>>>    				       data, (prior_data_len -
>>>
>>> frag_delta));
>>>
>>>> -				kunmap_atomic(vaddr);
>>>> +				kunmap_local(vaddr);
>>>>
>>>>    			}
>>>>    			/* reset tcp_seq as per the prior_data_required
>>>
>>> len */
>>>
>>>>    			tcp_seq -= prior_data_len;
>>>>
>>>> --
>>>> 2.37.2
>>>
>>> The last conversion could have been done with memcpy_from_page(). However,
>>> it's not that a big deal. Therefore...
>>>
>>> Reviewed-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
>>
>> Yeah, using memcpy_from_page() is cleaner. I'll update this patch, and
>> probably 4/5 too.
>>
>> Thanks!
>> Ani
> 
> Well, I didn't ask you for a second version. This is why you already see my
> "Reviewed-by:" tag. I'm OK with your changes. I just warned you that
> maintainers might ask, so I'd wait and see. However it's up to you.

I understand and appreciate your "Reviewed-by", but that doesn't mean 
further improvements aren't possible. I believe using memcpy_from_page() 
is better, and plan to do this in v2.

> 
> However, if you decide to send this patch with memcpy_from_page(), why you
> are not sure about 4/5? Since you decided to send 1/5 again, what does prevent
> you from updating also 4/5?

I hadn't seen patch 4/5 when I replied to you. Since then I have, and so 
I'll be updating 4/5 to use memcpy_from_page() as well.

Ani