xdp: rhashtable with allocator ID to pointer mapping

Use the IDA infrastructure for getting a cyclic increasing ID number,
that is used for keeping track of each registered allocator per
RX-queue xdp_rxq_info.  Instead of using the IDR infrastructure, which
uses a radix tree, use a dynamic rhashtable, for creating ID to
pointer lookup table, because this is faster.

The problem that is being solved here is that, the xdp_rxq_info
pointer (stored in xdp_buff) cannot be used directly, as the
guaranteed lifetime is too short.  The info is needed on a
(potentially) remote CPU during DMA-TX completion time . In an
xdp_frame the xdp_mem_info is stored, when it got converted from an
xdp_buff, which is sufficient for the simple page refcnt based recycle
schemes.

For more advanced allocators there is a need to store a pointer to the
registered allocator.  Thus, there is a need to guard the lifetime or
validity of the allocator pointer, which is done through this
rhashtable ID map to pointer. The removal and validity of of the
allocator and helper struct xdp_mem_allocator is guarded by RCU.  The
allocator will be created by the driver, and registered with
xdp_rxq_info_reg_mem_model().

It is up-to debate who is responsible for freeing the allocator
pointer or invoking the allocator destructor function.  In any case,
this must happen via RCU freeing.

Use the IDA infrastructure for getting a cyclic increasing ID number,
that is used for keeping track of each registered allocator per
RX-queue xdp_rxq_info.

V4: Per req of Jason Wang
- Use xdp_rxq_info_reg_mem_model() in all drivers implementing
  XDP_REDIRECT, even-though it's not strictly necessary when
  allocator==NULL for type MEM_TYPE_PAGE_SHARED (given it's zero).

V6: Per req of Alex Duyck
- Introduce rhashtable_lookup() call in later patch

V8: Address sparse should be static warnings (from kbuild test robot)

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 218 insertions, 5 deletions

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 7e6b3545277d..8b2cb79b5de0 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -5,6 +5,9 @@
  */
 #include <linux/types.h>
 #include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/idr.h>
+#include <linux/rhashtable.h>
 
 #include <net/xdp.h>
 
@@ -13,6 +16,99 @@
 #define REG_STATE_UNREGISTERED	0x2
 #define REG_STATE_UNUSED	0x3
 
+static DEFINE_IDA(mem_id_pool);
+static DEFINE_MUTEX(mem_id_lock);
+#define MEM_ID_MAX 0xFFFE
+#define MEM_ID_MIN 1
+static int mem_id_next = MEM_ID_MIN;
+
+static bool mem_id_init; /* false */
+static struct rhashtable *mem_id_ht;
+
+struct xdp_mem_allocator {
+	struct xdp_mem_info mem;
+	void *allocator;
+	struct rhash_head node;
+	struct rcu_head rcu;
+};
+
+static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
+{
+	const u32 *k = data;
+	const u32 key = *k;
+
+	BUILD_BUG_ON(FIELD_SIZEOF(struct xdp_mem_allocator, mem.id)
+		     != sizeof(u32));
+
+	/* Use cyclic increasing ID as direct hash key, see rht_bucket_index */
+	return key << RHT_HASH_RESERVED_SPACE;
+}
+
+static int xdp_mem_id_cmp(struct rhashtable_compare_arg *arg,
+			  const void *ptr)
+{
+	const struct xdp_mem_allocator *xa = ptr;
+	u32 mem_id = *(u32 *)arg->key;
+
+	return xa->mem.id != mem_id;
+}
+
+static const struct rhashtable_params mem_id_rht_params = {
+	.nelem_hint = 64,
+	.head_offset = offsetof(struct xdp_mem_allocator, node),
+	.key_offset  = offsetof(struct xdp_mem_allocator, mem.id),
+	.key_len = FIELD_SIZEOF(struct xdp_mem_allocator, mem.id),
+	.max_size = MEM_ID_MAX,
+	.min_size = 8,
+	.automatic_shrinking = true,
+	.hashfn    = xdp_mem_id_hashfn,
+	.obj_cmpfn = xdp_mem_id_cmp,
+};
+
+static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
+{
+	struct xdp_mem_allocator *xa;
+
+	xa = container_of(rcu, struct xdp_mem_allocator, rcu);
+
+	/* Allow this ID to be reused */
+	ida_simple_remove(&mem_id_pool, xa->mem.id);
+
+	/* TODO: Depending on allocator type/pointer free resources */
+
+	/* Poison memory */
+	xa->mem.id = 0xFFFF;
+	xa->mem.type = 0xF0F0;
+	xa->allocator = (void *)0xDEAD9001;
+
+	kfree(xa);
+}
+
+static void __xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
+{
+	struct xdp_mem_allocator *xa;
+	int id = xdp_rxq->mem.id;
+	int err;
+
+	if (id == 0)
+		return;
+
+	mutex_lock(&mem_id_lock);
+
+	xa = rhashtable_lookup(mem_id_ht, &id, mem_id_rht_params);
+	if (!xa) {
+		mutex_unlock(&mem_id_lock);
+		return;
+	}
+
+	err = rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params);
+	WARN_ON(err);
+
+	call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
+
+	mutex_unlock(&mem_id_lock);
+}
+
 void xdp_rxq_info_unreg(struct xdp_rxq_info *xdp_rxq)
 {
 	/* Simplify driver cleanup code paths, allow unreg "unused" */
@@ -21,8 +117,14 @@ void xdp_rxq_info_unreg(struct xdp_rxq_info *xdp_rxq)
 
 	WARN(!(xdp_rxq->reg_state == REG_STATE_REGISTERED), "Driver BUG");
 
+	__xdp_rxq_info_unreg_mem_model(xdp_rxq);
+
 	xdp_rxq->reg_state = REG_STATE_UNREGISTERED;
 	xdp_rxq->dev = NULL;
+
+	/* Reset mem info to defaults */
+	xdp_rxq->mem.id = 0;
+	xdp_rxq->mem.type = 0;
 }
 EXPORT_SYMBOL_GPL(xdp_rxq_info_unreg);
 
@@ -72,20 +174,131 @@ bool xdp_rxq_info_is_reg(struct xdp_rxq_info *xdp_rxq)
 }
 EXPORT_SYMBOL_GPL(xdp_rxq_info_is_reg);
 
+static int __mem_id_init_hash_table(void)
+{
+	struct rhashtable *rht;
+	int ret;
+
+	if (unlikely(mem_id_init))
+		return 0;
+
+	rht = kzalloc(sizeof(*rht), GFP_KERNEL);
+	if (!rht)
+		return -ENOMEM;
+
+	ret = rhashtable_init(rht, &mem_id_rht_params);
+	if (ret < 0) {
+		kfree(rht);
+		return ret;
+	}
+	mem_id_ht = rht;
+	smp_mb(); /* mutex lock should provide enough pairing */
+	mem_id_init = true;
+
+	return 0;
+}
+
+/* Allocate a cyclic ID that maps to allocator pointer.
+ * See: https://www.kernel.org/doc/html/latest/core-api/idr.html
+ *
+ * Caller must lock mem_id_lock.
+ */
+static int __mem_id_cyclic_get(gfp_t gfp)
+{
+	int retries = 1;
+	int id;
+
+again:
+	id = ida_simple_get(&mem_id_pool, mem_id_next, MEM_ID_MAX, gfp);
+	if (id < 0) {
+		if (id == -ENOSPC) {
+			/* Cyclic allocator, reset next id */
+			if (retries--) {
+				mem_id_next = MEM_ID_MIN;
+				goto again;
+			}
+		}
+		return id; /* errno */
+	}
+	mem_id_next = id + 1;
+
+	return id;
+}
+
 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;
+	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 (type >= MEM_TYPE_MAX)
 		return -EINVAL;
 
 	xdp_rxq->mem.type = type;
 
-	if (allocator)
-		return -EOPNOTSUPP;
+	if (!allocator)
+		return 0;
+
+	/* Delay init of rhashtable to save memory if feature isn't used */
+	if (!mem_id_init) {
+		mutex_lock(&mem_id_lock);
+		ret = __mem_id_init_hash_table();
+		mutex_unlock(&mem_id_lock);
+		if (ret < 0) {
+			WARN_ON(1);
+			return ret;
+		}
+	}
+
+	xdp_alloc = kzalloc(sizeof(*xdp_alloc), gfp);
+	if (!xdp_alloc)
+		return -ENOMEM;
+
+	mutex_lock(&mem_id_lock);
+	id = __mem_id_cyclic_get(gfp);
+	if (id < 0) {
+		errno = id;
+		goto err;
+	}
+	xdp_rxq->mem.id = id;
+	xdp_alloc->mem  = xdp_rxq->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)) {
+		errno = PTR_ERR(ptr);
+		goto err;
+	}
+
+	mutex_unlock(&mem_id_lock);
 
-	/* TODO: Allocate an ID that maps to allocator pointer
-	 * See: https://www.kernel.org/doc/html/latest/core-api/idr.html
-	 */
 	return 0;
+err:
+	mutex_unlock(&mem_id_lock);
+	kfree(xdp_alloc);
+	return errno;
 }
 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) {
+		page_frag_free(data);
+		return;
+	}
+
+	if (mem->type == MEM_TYPE_PAGE_ORDER0) {
+		struct page *page = virt_to_page(data); /* Assumes order0 page*/
+
+		put_page(page);
+	}
+}
+EXPORT_SYMBOL_GPL(xdp_return_frame);