xdp: implement convert_to_xdp_frame for MEM_TYPE_ZERO_COPY

This commit adds proper MEM_TYPE_ZERO_COPY support for
convert_to_xdp_frame. Converting a MEM_TYPE_ZERO_COPY xdp_buff to an
xdp_frame is done by transforming the MEM_TYPE_ZERO_COPY buffer into a
MEM_TYPE_PAGE_ORDER0 frame. This is costly, and in the future it might
make sense to implement a more sophisticated thread-safe alloc/free
scheme for MEM_TYPE_ZERO_COPY, so that no allocation and copy is
required in the fast-path.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/net/xdp.h

@@ -91,6 +91,8 @@ static inline void xdp_scrub_frame(struct xdp_frame *frame)
 	frame->dev_rx = NULL;
 }
 
+struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp);
+
 /* Convert xdp_buff to xdp_frame */
 static inline
 struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp)
@@ -99,9 +101,8 @@ struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp)
 	int metasize;
 	int headroom;
 
-	/* TODO: implement clone, copy, use "native" MEM_TYPE */
 	if (xdp->rxq->mem.type == MEM_TYPE_ZERO_COPY)
-		return NULL;
+		return xdp_convert_zc_to_xdp_frame(xdp);
 
 	/* Assure headroom is available for storing info */
 	headroom = xdp->data - xdp->data_hard_start;

net/core/xdp.c

@@ -398,3 +398,42 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
 	info->flags = bpf->flags;
 }
 EXPORT_SYMBOL_GPL(xdp_attachment_setup);
+
+struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp)
+{
+	unsigned int metasize, headroom, totsize;
+	void *addr, *data_to_copy;
+	struct xdp_frame *xdpf;
+	struct page *page;
+
+	/* Clone into a MEM_TYPE_PAGE_ORDER0 xdp_frame. */
+	metasize = xdp_data_meta_unsupported(xdp) ? 0 :
+		   xdp->data - xdp->data_meta;
+	headroom = xdp->data - xdp->data_hard_start;
+	totsize = xdp->data_end - xdp->data + metasize;
+
+	if (sizeof(*xdpf) + totsize > PAGE_SIZE)
+		return NULL;
+
+	page = dev_alloc_page();
+	if (!page)
+		return NULL;
+
+	addr = page_to_virt(page);
+	xdpf = addr;
+	memset(xdpf, 0, sizeof(*xdpf));
+
+	addr += sizeof(*xdpf);
+	data_to_copy = metasize ? xdp->data_meta : xdp->data;
+	memcpy(addr, data_to_copy, totsize);
+
+	xdpf->data = addr + metasize;
+	xdpf->len = totsize - metasize;
+	xdpf->headroom = 0;
+	xdpf->metasize = metasize;
+	xdpf->mem.type = MEM_TYPE_PAGE_ORDER0;
+
+	xdp_return_buff(xdp);
+	return xdpf;
+}
+EXPORT_SYMBOL_GPL(xdp_convert_zc_to_xdp_frame);