[bpf-next V6 PATCH 12/15] xdp: allow page_pool as an allocator type in xdp_return_frame

[Jesper Dangaard Brouer <brouer@redhat.com>]

New allocator type MEM_TYPE_PAGE_POOL for page_pool usage.

The registered allocator page_pool pointer is not available directly
from xdp_rxq_info, but it could be (if needed).  For now, the driver
should keep separate track of the page_pool pointer, which it should
use for RX-ring page allocation.

As suggested by Saeed, to maintain a symmetric API it is the drivers
responsibility to allocate/create and free/destroy the page_pool.
Thus, after the driver have called xdp_rxq_info_unreg(), it is drivers
responsibility to free the page_pool, but with a RCU free call.  This
is done easily via the page_pool helper page_pool_destroy() (which
avoids touching any driver code during the RCU callback, which could
happen after the driver have been unloaded).

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 include/net/xdp.h |    3 +++
 net/core/xdp.c    |   45 +++++++++++++++++++++++++++++++++++----------
 2 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 859aa9b737fe..98b55eaf8fd7 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -36,6 +36,7 @@
 enum mem_type {
 	MEM_TYPE_PAGE_SHARED = 0, /* Split-page refcnt based model */
 	MEM_TYPE_PAGE_ORDER0,     /* Orig XDP full page model */
+	MEM_TYPE_PAGE_POOL,
 	MEM_TYPE_MAX,
 };
 
@@ -44,6 +45,8 @@ struct xdp_mem_info {
 	u32 id;
 };
 
+struct page_pool;
+
 struct xdp_rxq_info {
 	struct net_device *dev;
 	u32 queue_index;
diff --git a/net/core/xdp.c b/net/core/xdp.c
index e7f11f05086d..cc3238474e8c 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -8,6 +8,7 @@
 #include <linux/slab.h>
 #include <linux/idr.h>
 #include <linux/rhashtable.h>
+#include <net/page_pool.h>
 
 #include <net/xdp.h>
 
@@ -27,7 +28,10 @@ static struct rhashtable *mem_id_ht;
 
 struct xdp_mem_allocator {
 	struct xdp_mem_info mem;
-	void *allocator;
+	union {
+		void *allocator;
+		struct page_pool *page_pool;
+	};
 	struct rhash_head node;
 	struct rcu_head rcu;
 };
@@ -74,7 +78,9 @@ void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
 	/* Allow this ID to be reused */
 	ida_simple_remove(&mem_id_pool, xa->mem.id);
 
-	/* TODO: Depending on allocator type/pointer free resources */
+	/* Notice, driver is expected to free the *allocator,
+	 * e.g. page_pool, and MUST also use RCU free.
+	 */
 
 	/* Poison memory */
 	xa->mem.id = 0xFFFF;
@@ -243,8 +249,11 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 
 	xdp_rxq->mem.type = type;
 
-	if (!allocator)
+	if (!allocator) {
+		if (type == MEM_TYPE_PAGE_POOL)
+			return -EINVAL; /* Setup time check page_pool req */
 		return 0;
+	}
 
 	/* Delay init of rhashtable to save memory if feature isn't used */
 	if (!mem_id_init) {
@@ -290,15 +299,31 @@ EXPORT_SYMBOL_GPL(xdp_rxq_info_reg_mem_model);
 
 void xdp_return_frame(void *data, struct xdp_mem_info *mem)
 {
-	if (mem->type == MEM_TYPE_PAGE_SHARED) {
+	struct xdp_mem_allocator *xa;
+	struct page *page;
+
+	switch (mem->type) {
+	case MEM_TYPE_PAGE_POOL:
+		rcu_read_lock();
+		/* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
+		xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
+		page = virt_to_head_page(data);
+		if (xa)
+			page_pool_put_page(xa->page_pool, page);
+		else
+			put_page(page);
+		rcu_read_unlock();
+		break;
+	case MEM_TYPE_PAGE_SHARED:
 		page_frag_free(data);
-		return;
-	}
-
-	if (mem->type == MEM_TYPE_PAGE_ORDER0) {
-		struct page *page = virt_to_page(data); /* Assumes order0 page*/
-
+		break;
+	case MEM_TYPE_PAGE_ORDER0:
+		page = virt_to_page(data); /* Assumes order0 page*/
 		put_page(page);
+		break;
+	default:
+		/* Not possible, checked in xdp_rxq_info_reg_mem_model() */
+		break;
 	}
 }
 EXPORT_SYMBOL_GPL(xdp_return_frame);