Re: [PATCH net-next v5 4/9] xen-netback: Change RX path for mapped SKB fragments

[Ian Campbell <Ian.Campbell@citrix.com>]

On Mon, 2014-01-20 at 21:24 +0000, Zoltan Kiss wrote:

Re the Subject: change how? Perhaps "handle foreign mapped pages on the
guest RX path" would be clearer.

> RX path need to know if the SKB fragments are stored on pages from another
> domain.

Does this not need to be done either before the mapping change or at the
same time? -- otherwise you have a window of a couple of commits where
things are broken, breaking bisectability.

> 
> v4:
> - indentation fixes
> 
> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
> ---
>  drivers/net/xen-netback/netback.c |   46 +++++++++++++++++++++++++++++++++----
>  1 file changed, 41 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index f74fa92..d43444d 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -226,7 +226,9 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
>  static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
>  				 struct netrx_pending_operations *npo,
>  				 struct page *page, unsigned long size,
> -				 unsigned long offset, int *head)
> +				 unsigned long offset, int *head,
> +				 struct xenvif *foreign_vif,
> +				 grant_ref_t foreign_gref)
>  {
>  	struct gnttab_copy *copy_gop;
>  	struct xenvif_rx_meta *meta;
> @@ -268,8 +270,15 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
>  		copy_gop->flags = GNTCOPY_dest_gref;
>  		copy_gop->len = bytes;
>  
> -		copy_gop->source.domid = DOMID_SELF;
> -		copy_gop->source.u.gmfn = virt_to_mfn(page_address(page));
> +		if (foreign_vif) {
> +			copy_gop->source.domid = foreign_vif->domid;
> +			copy_gop->source.u.ref = foreign_gref;
> +			copy_gop->flags |= GNTCOPY_source_gref;
> +		} else {
> +			copy_gop->source.domid = DOMID_SELF;
> +			copy_gop->source.u.gmfn =
> +				virt_to_mfn(page_address(page));
> +		}
>  		copy_gop->source.offset = offset;
>  
>  		copy_gop->dest.domid = vif->domid;
> @@ -330,6 +339,9 @@ static int xenvif_gop_skb(struct sk_buff *skb,
>  	int old_meta_prod;
>  	int gso_type;
>  	int gso_size;
> +	struct ubuf_info *ubuf = skb_shinfo(skb)->destructor_arg;
> +	grant_ref_t foreign_grefs[MAX_SKB_FRAGS];
> +	struct xenvif *foreign_vif = NULL;
>  
>  	old_meta_prod = npo->meta_prod;
>  
> @@ -370,6 +382,26 @@ static int xenvif_gop_skb(struct sk_buff *skb,
>  	npo->copy_off = 0;
>  	npo->copy_gref = req->gref;
>  
> +	if ((skb_shinfo(skb)->tx_flags & SKBTX_DEV_ZEROCOPY) &&
> +		 (ubuf->callback == &xenvif_zerocopy_callback)) {
> +		u16 pending_idx = ubuf->desc;
> +		int i = 0;
> +		struct pending_tx_info *temp =
> +			container_of(ubuf,
> +				     struct pending_tx_info,
> +				     callback_struct);
> +		foreign_vif =
> +			container_of(temp - pending_idx,
> +				     struct xenvif,
> +				     pending_tx_info[0]);
> +		do {
> +			pending_idx = ubuf->desc;
> +			foreign_grefs[i++] =
> +				foreign_vif->pending_tx_info[pending_idx].req.gref;
> +			ubuf = (struct ubuf_info *) ubuf->ctx;
> +		} while (ubuf);
> +	}
> +
>  	data = skb->data;
>  	while (data < skb_tail_pointer(skb)) {
>  		unsigned int offset = offset_in_page(data);
> @@ -379,7 +411,9 @@ static int xenvif_gop_skb(struct sk_buff *skb,
>  			len = skb_tail_pointer(skb) - data;
>  
>  		xenvif_gop_frag_copy(vif, skb, npo,
> -				     virt_to_page(data), len, offset, &head);
> +				     virt_to_page(data), len, offset, &head,
> +				     NULL,
> +				     0);
>  		data += len;
>  	}
>  
> @@ -388,7 +422,9 @@ static int xenvif_gop_skb(struct sk_buff *skb,
>  				     skb_frag_page(&skb_shinfo(skb)->frags[i]),
>  				     skb_frag_size(&skb_shinfo(skb)->frags[i]),
>  				     skb_shinfo(skb)->frags[i].page_offset,
> -				     &head);
> +				     &head,
> +				     foreign_vif,
> +				     foreign_grefs[i]);
>  	}
>  
>  	return npo->meta_prod - old_meta_prod;