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

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Date:   Thu, 24 Nov 2022 16:26:42 +0530
From:   Ayush Sawal <ayush.sawal@...lsio.com>
To:     Anirudh Venkataramanan <anirudh.venkataramanan@...el.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 2:22 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>

>   .../chelsio/inline_crypto/ch_ktls/chcr_ktls.c | 26 +++++++++----------
>   1 file changed, 12 insertions(+), 14 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..1a5fdd7 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
> @@ -1839,9 +1839,7 @@ static int chcr_short_record_handler(struct chcr_ktls_info *tx_info,
>   		 */
>   		if (prior_data_len) {
>   			int i = 0;
> -			u8 *data = NULL;
>   			skb_frag_t *f;
> -			u8 *vaddr;
>   			int frag_size = 0, frag_delta = 0;
>   
>   			while (remaining > 0) {
> @@ -1853,24 +1851,24 @@ static int chcr_short_record_handler(struct chcr_ktls_info *tx_info,
>   				i++;
>   			}
>   			f = &record->frags[i];
> -			vaddr = kmap_atomic(skb_frag_page(f));
> -
> -			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);
> +				memcpy_from_page(prior_data, skb_frag_page(f),
> +						 skb_frag_off(f) + remaining,
> +						 prior_data_len);
>   			} else {
> -				memcpy(prior_data, data, frag_delta);
> -				kunmap_atomic(vaddr);
> +				memcpy_from_page(prior_data, skb_frag_page(f),
> +						 skb_frag_off(f) + remaining,
> +						 frag_delta);
> +
>   				/* get the next page */
>   				f = &record->frags[i + 1];
> -				vaddr = kmap_atomic(skb_frag_page(f));
> -				data = vaddr + skb_frag_off(f);
> -				memcpy(prior_data + frag_delta,
> -				       data, (prior_data_len - frag_delta));
> -				kunmap_atomic(vaddr);
> +
> +				memcpy_from_page(prior_data + frag_delta,
> +						 skb_frag_page(f),
> +						 skb_frag_off(f),
> +						 prior_data_len - frag_delta);
>   			}
>   			/* reset tcp_seq as per the prior_data_required len */
>   			tcp_seq -= prior_data_len;

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