xdp: Allow registering memory model without rxq reference

The functions that register an XDP memory model take a struct xdp_rxq as
parameter, but the RXQ is not actually used for anything other than pulling
out the struct xdp_mem_info that it embeds. So refactor the register
functions and export variants that just take a pointer to the xdp_mem_info.

This is in preparation for enabling XDP_REDIRECT in bpf_prog_run(), using a
page_pool instance that is not connected to any network device.
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220103150812.87914-2-toke@redhat.com

include/net/xdp.h

@@ -260,6 +260,9 @@ bool xdp_rxq_info_is_reg(struct xdp_rxq_info *xdp_rxq);
 int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 			       enum xdp_mem_type type, void *allocator);
 void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq);
+int xdp_reg_mem_model(struct xdp_mem_info *mem,
+		      enum xdp_mem_type type, void *allocator);
+void xdp_unreg_mem_model(struct xdp_mem_info *mem);
 
 /* Drivers not supporting XDP metadata can use this helper, which
  * rejects any room expansion for metadata as a result.

net/core/xdp.c

@@ -110,20 +110,15 @@ static void mem_allocator_disconnect(void *allocator)
 	mutex_unlock(&mem_id_lock);
 }
 
-void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
+void xdp_unreg_mem_model(struct xdp_mem_info *mem)
 {
 	struct xdp_mem_allocator *xa;
-	int type = xdp_rxq->mem.type;
-	int id = xdp_rxq->mem.id;
+	int type = mem->type;
+	int id = mem->id;
 
 	/* Reset mem info to defaults */
-	xdp_rxq->mem.id = 0;
-	xdp_rxq->mem.type = 0;
-
-	if (xdp_rxq->reg_state != REG_STATE_REGISTERED) {
-		WARN(1, "Missing register, driver bug");
-		return;
-	}
+	mem->id = 0;
+	mem->type = 0;
 
 	if (id == 0)
 		return;
@@ -135,6 +130,17 @@ void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
 		rcu_read_unlock();
 	}
 }
+EXPORT_SYMBOL_GPL(xdp_unreg_mem_model);
+
+void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
+{
+	if (xdp_rxq->reg_state != REG_STATE_REGISTERED) {
+		WARN(1, "Missing register, driver bug");
+		return;
+	}
+
+	xdp_unreg_mem_model(&xdp_rxq->mem);
+}
 EXPORT_SYMBOL_GPL(xdp_rxq_info_unreg_mem_model);
 
 void xdp_rxq_info_unreg(struct xdp_rxq_info *xdp_rxq)
@@ -259,28 +265,24 @@ static bool __is_supported_mem_type(enum xdp_mem_type type)
 	return true;
 }
 
-int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
-			       enum xdp_mem_type type, void *allocator)
+static struct xdp_mem_allocator *__xdp_reg_mem_model(struct xdp_mem_info *mem,
+						     enum xdp_mem_type type,
+						     void *allocator)
 {
 	struct xdp_mem_allocator *xdp_alloc;
 	gfp_t gfp = GFP_KERNEL;
 	int id, errno, ret;
 	void *ptr;
 
-	if (xdp_rxq->reg_state != REG_STATE_REGISTERED) {
-		WARN(1, "Missing register, driver bug");
-		return -EFAULT;
-	}
-
 	if (!__is_supported_mem_type(type))
-		return -EOPNOTSUPP;
+		return ERR_PTR(-EOPNOTSUPP);
 
-	xdp_rxq->mem.type = type;
+	mem->type = type;
 
 	if (!allocator) {
 		if (type == MEM_TYPE_PAGE_POOL)
-			return -EINVAL; /* Setup time check page_pool req */
-		return 0;
+			return ERR_PTR(-EINVAL); /* Setup time check page_pool req */
+		return NULL;
 	}
 
 	/* Delay init of rhashtable to save memory if feature isn't used */
@@ -290,13 +292,13 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 		mutex_unlock(&mem_id_lock);
 		if (ret < 0) {
 			WARN_ON(1);
-			return ret;
+			return ERR_PTR(ret);
 		}
 	}
 
 	xdp_alloc = kzalloc(sizeof(*xdp_alloc), gfp);
 	if (!xdp_alloc)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	mutex_lock(&mem_id_lock);
 	id = __mem_id_cyclic_get(gfp);
@@ -304,15 +306,15 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 		errno = id;
 		goto err;
 	}
-	xdp_rxq->mem.id = id;
-	xdp_alloc->mem  = xdp_rxq->mem;
+	mem->id = id;
+	xdp_alloc->mem = *mem;
 	xdp_alloc->allocator = allocator;
 
 	/* Insert allocator into ID lookup table */
 	ptr = rhashtable_insert_slow(mem_id_ht, &id, &xdp_alloc->node);
 	if (IS_ERR(ptr)) {
-		ida_simple_remove(&mem_id_pool, xdp_rxq->mem.id);
-		xdp_rxq->mem.id = 0;
+		ida_simple_remove(&mem_id_pool, mem->id);
+		mem->id = 0;
 		errno = PTR_ERR(ptr);
 		goto err;
 	}
@@ -322,13 +324,43 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 
 	mutex_unlock(&mem_id_lock);
 
-	trace_mem_connect(xdp_alloc, xdp_rxq);
-	return 0;
+	return xdp_alloc;
 err:
 	mutex_unlock(&mem_id_lock);
 	kfree(xdp_alloc);
-	return errno;
+	return ERR_PTR(errno);
+}
+
+int xdp_reg_mem_model(struct xdp_mem_info *mem,
+		      enum xdp_mem_type type, void *allocator)
+{
+	struct xdp_mem_allocator *xdp_alloc;
+
+	xdp_alloc = __xdp_reg_mem_model(mem, type, allocator);
+	if (IS_ERR(xdp_alloc))
+		return PTR_ERR(xdp_alloc);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(xdp_reg_mem_model);
+
+int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
+			       enum xdp_mem_type type, void *allocator)
+{
+	struct xdp_mem_allocator *xdp_alloc;
+
+	if (xdp_rxq->reg_state != REG_STATE_REGISTERED) {
+		WARN(1, "Missing register, driver bug");
+		return -EFAULT;
+	}
+
+	xdp_alloc = __xdp_reg_mem_model(&xdp_rxq->mem, type, allocator);
+	if (IS_ERR(xdp_alloc))
+		return PTR_ERR(xdp_alloc);
+
+	trace_mem_connect(xdp_alloc, xdp_rxq);
+	return 0;
 }
+
 EXPORT_SYMBOL_GPL(xdp_rxq_info_reg_mem_model);
 
 /* XDP RX runs under NAPI protection, and in different delivery error