Subject: Re: [PATCH v2 net-next 5/6] sunvnet: Use kmap_local_page() instead of kmap_atomic()

From: "Fabio M. De Francesco" <[email-masked]>
Date: Fri, 25 Nov 2022 16:40:05 +0100

On mercoledì 23 novembre 2022 21:52:18 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. 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 kmap_local_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 as opposed to page_address().
> 
> I don't have hardware, so this change has only been compile tested.
> 
> Cc: Ira Weiny <[email-masked]>
> Cc: Fabio M. De Francesco <[email-masked]>
> Signed-off-by: Anirudh Venkataramanan <[email-masked]>
> ---
> v1 -> v2: Update commit message
> ---
>  drivers/net/ethernet/sun/sunvnet_common.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Fabio M. De Francesco <[email-masked]>

Thanks,

Fabio

> diff --git a/drivers/net/ethernet/sun/sunvnet_common.c
> b/drivers/net/ethernet/sun/sunvnet_common.c index 80fde5f..a6211b9 100644
> --- a/drivers/net/ethernet/sun/sunvnet_common.c
> +++ b/drivers/net/ethernet/sun/sunvnet_common.c
> @@ -1085,13 +1085,13 @@ static inline int vnet_skb_map(struct ldc_channel 
*lp,
> struct sk_buff *skb, u8 *vaddr;
> 
>  		if (nc < ncookies) {
> -			vaddr = kmap_atomic(skb_frag_page(f));
> +			vaddr = kmap_local_page(skb_frag_page(f));
>  			blen = skb_frag_size(f);
>  			blen += 8 - (blen & 7);
>  			err = ldc_map_single(lp, vaddr + 
skb_frag_off(f),
>  					     blen, cookies + nc, 
ncookies - nc,
>  					     map_perm);
> -			kunmap_atomic(vaddr);
> +			kunmap_local(vaddr);
>  		} else {
>  			err = -EMSGSIZE;
>  		}
> --
> 2.37.2