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 09:14:20 +0100
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     netdev@...r.kernel.org,
        Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Anirudh Venkataramanan <anirudh.venkataramanan@...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 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>

Thanks,

Fabio