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

From: "Fabio M. De Francesco" <[email-masked]>
Date: Fri, 18 Nov 2022 21:18:56 +0100

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 <[email-masked]>
> >> Cc: Vinay Kumar Yadav <[email-masked]>
> >> Cc: Rohit Maheshwari <[email-masked]>
> >> Cc: Ira Weiny <[email-masked]>
> >> Cc: Fabio M. De Francesco <[email-masked]>
> >> Signed-off-by: Anirudh Venkataramanan <[email-masked]>
> >> ---
> >> 
> >>   .../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 <[email-masked]>
> 
> 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.

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?

Fabio