Subject: Re: [net-next PATCH v9 1/8] octeontx2-pf: map skb data as device writeable

From: Leon Romanovsky <[email-masked]>
Date: Sun, 10 Nov 2024 16:23:03 +0200

On Fri, Nov 08, 2024 at 10:27:01AM +0530, Bharat Bhushan wrote:
> Crypto hardware need write permission for in-place encrypt
> or decrypt operation on skb-data to support IPsec crypto
> offload. That patch uses skb_unshare to make skb data writeable
> for ipsec crypto offload and map skb fragment memory as
> device read-write.
> 
> Signed-off-by: Bharat Bhushan <[email-masked]>
> ---
> v7->v8:
>  - spell correction (s/sdk/skb) in description
> 
> v6->v7:
>  - skb data was mapped as device writeable but it was not ensured
>    that skb is writeable. This version calls skb_unshare() to make
>    skb data writeable.
> 
>  .../ethernet/marvell/octeontx2/nic/otx2_txrx.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c
> index 7aaf32e9aa95..49b6b091ba41 100644
> --- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c
> +++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c
> @@ -11,6 +11,7 @@
>  #include <linux/bpf.h>
>  #include <linux/bpf_trace.h>
>  #include <net/ip6_checksum.h>
> +#include <net/xfrm.h>
>  
>  #include "otx2_reg.h"
>  #include "otx2_common.h"
> @@ -83,10 +84,17 @@ static unsigned int frag_num(unsigned int i)
>  static dma_addr_t otx2_dma_map_skb_frag(struct otx2_nic *pfvf,
>  					struct sk_buff *skb, int seg, int *len)
>  {
> +	enum dma_data_direction dir = DMA_TO_DEVICE;
>  	const skb_frag_t *frag;
>  	struct page *page;
>  	int offset;
>  
> +	/* Crypto hardware need write permission for ipsec crypto offload */
> +	if (unlikely(xfrm_offload(skb))) {
> +		dir = DMA_BIDIRECTIONAL;
> +		skb = skb_unshare(skb, GFP_ATOMIC);
> +	}
> +
>  	/* First segment is always skb->data */
>  	if (!seg) {
>  		page = virt_to_page(skb->data);
> @@ -98,16 +106,22 @@ static dma_addr_t otx2_dma_map_skb_frag(struct otx2_nic *pfvf,
>  		offset = skb_frag_off(frag);
>  		*len = skb_frag_size(frag);
>  	}
> -	return otx2_dma_map_page(pfvf, page, offset, *len, DMA_TO_DEVICE);
> +	return otx2_dma_map_page(pfvf, page, offset, *len, dir);

Did I read correctly and you perform DMA mapping on every SKB in data path?
How bad does it perform if you enable IOMMU?

Thanks

>  }
>  
>  static void otx2_dma_unmap_skb_frags(struct otx2_nic *pfvf, struct sg_list *sg)
>  {
> +	enum dma_data_direction dir = DMA_TO_DEVICE;
> +	struct sk_buff *skb = NULL;
>  	int seg;
>  
> +	skb = (struct sk_buff *)sg->skb;
> +	if (unlikely(xfrm_offload(skb)))
> +		dir = DMA_BIDIRECTIONAL;
> +
>  	for (seg = 0; seg < sg->num_segs; seg++) {
>  		otx2_dma_unmap_page(pfvf, sg->dma_addr[seg],
> -				    sg->size[seg], DMA_TO_DEVICE);
> +				    sg->size[seg], dir);
>  	}
>  	sg->num_segs = 0;
>  }
> -- 
> 2.34.1
> 
>