xsk: new descriptor addressing scheme

Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data.  Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).

By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.

In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.

In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.

We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.

To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.

On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.

Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.

This commit changes the uapi of AF_XDP sockets, and updates the
documentation.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 19 insertions, 24 deletions

diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index b5924e7aeb2b..337e5ad3b10e 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -27,7 +27,7 @@ struct xdp_rxtx_ring {
 /* Used for the fill and completion queues for buffers */
 struct xdp_umem_ring {
 	struct xdp_ring ptrs;
-	u32 desc[0] ____cacheline_aligned_in_smp;
+	u64 desc[0] ____cacheline_aligned_in_smp;
 };
 
 struct xsk_queue {
@@ -76,24 +76,25 @@ static inline u32 xskq_nb_free(struct xsk_queue *q, u32 producer, u32 dcnt)
 
 /* UMEM queue */
 
-static inline bool xskq_is_valid_id(struct xsk_queue *q, u32 idx)
+static inline bool xskq_is_valid_addr(struct xsk_queue *q, u64 addr)
 {
-	if (unlikely(idx >= q->umem_props.nframes)) {
+	if (addr >= q->umem_props.size) {
 		q->invalid_descs++;
 		return false;
 	}
+
 	return true;
 }
 
-static inline u32 *xskq_validate_id(struct xsk_queue *q, u32 *id)
+static inline u64 *xskq_validate_addr(struct xsk_queue *q, u64 *addr)
 {
 	while (q->cons_tail != q->cons_head) {
 		struct xdp_umem_ring *ring = (struct xdp_umem_ring *)q->ring;
 		unsigned int idx = q->cons_tail & q->ring_mask;
 
-		*id = READ_ONCE(ring->desc[idx]);
-		if (xskq_is_valid_id(q, *id))
-			return id;
+		*addr = READ_ONCE(ring->desc[idx]) & q->umem_props.chunk_mask;
+		if (xskq_is_valid_addr(q, *addr))
+			return addr;
 
 		q->cons_tail++;
 	}
@@ -101,7 +102,7 @@ static inline u32 *xskq_validate_id(struct xsk_queue *q, u32 *id)
 	return NULL;
 }
 
-static inline u32 *xskq_peek_id(struct xsk_queue *q, u32 *id)
+static inline u64 *xskq_peek_addr(struct xsk_queue *q, u64 *addr)
 {
 	if (q->cons_tail == q->cons_head) {
 		WRITE_ONCE(q->ring->consumer, q->cons_tail);
@@ -111,19 +112,19 @@ static inline u32 *xskq_peek_id(struct xsk_queue *q, u32 *id)
 		smp_rmb();
 	}
 
-	return xskq_validate_id(q, id);
+	return xskq_validate_addr(q, addr);
 }
 
-static inline void xskq_discard_id(struct xsk_queue *q)
+static inline void xskq_discard_addr(struct xsk_queue *q)
 {
 	q->cons_tail++;
 }
 
-static inline int xskq_produce_id(struct xsk_queue *q, u32 id)
+static inline int xskq_produce_addr(struct xsk_queue *q, u64 addr)
 {
 	struct xdp_umem_ring *ring = (struct xdp_umem_ring *)q->ring;
 
-	ring->desc[q->prod_tail++ & q->ring_mask] = id;
+	ring->desc[q->prod_tail++ & q->ring_mask] = addr;
 
 	/* Order producer and data */
 	smp_wmb();
@@ -132,7 +133,7 @@ static inline int xskq_produce_id(struct xsk_queue *q, u32 id)
 	return 0;
 }
 
-static inline int xskq_reserve_id(struct xsk_queue *q)
+static inline int xskq_reserve_addr(struct xsk_queue *q)
 {
 	if (xskq_nb_free(q, q->prod_head, 1) == 0)
 		return -ENOSPC;
@@ -145,16 +146,11 @@ static inline int xskq_reserve_id(struct xsk_queue *q)
 
 static inline bool xskq_is_valid_desc(struct xsk_queue *q, struct xdp_desc *d)
 {
-	u32 buff_len;
-
-	if (unlikely(d->idx >= q->umem_props.nframes)) {
-		q->invalid_descs++;
+	if (!xskq_is_valid_addr(q, d->addr))
 		return false;
-	}
 
-	buff_len = q->umem_props.frame_size;
-	if (unlikely(d->len > buff_len || d->len == 0 ||
-		     d->offset > buff_len || d->offset + d->len > buff_len)) {
+	if (((d->addr + d->len) & q->umem_props.chunk_mask) !=
+	    (d->addr & q->umem_props.chunk_mask)) {
 		q->invalid_descs++;
 		return false;
 	}
@@ -199,7 +195,7 @@ static inline void xskq_discard_desc(struct xsk_queue *q)
 }
 
 static inline int xskq_produce_batch_desc(struct xsk_queue *q,
-					  u32 id, u32 len, u16 offset)
+					  u64 addr, u32 len)
 {
 	struct xdp_rxtx_ring *ring = (struct xdp_rxtx_ring *)q->ring;
 	unsigned int idx;
@@ -208,9 +204,8 @@ static inline int xskq_produce_batch_desc(struct xsk_queue *q,
 		return -ENOSPC;
 
 	idx = (q->prod_head++) & q->ring_mask;
-	ring->desc[idx].idx = id;
+	ring->desc[idx].addr = addr;
 	ring->desc[idx].len = len;
-	ring->desc[idx].offset = offset;
 
 	return 0;
 }