1 files changed, 95 insertions, 19 deletions

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index d706c4b7f532..f6a075ffac63 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -13,7 +13,7 @@
 #include <linux/btf_ids.h>
 #include <asm/rqspinlock.h>
 
-#define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE)
+#define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE | BPF_F_RB_OVERWRITE)
 
 /* non-mmap()'able part of bpf_ringbuf (everything up to consumer page) */
 #define RINGBUF_PGOFF \
@@ -30,6 +30,7 @@ struct bpf_ringbuf {
 	u64 mask;
 	struct page **pages;
 	int nr_pages;
+	bool overwrite_mode;
 	rqspinlock_t spinlock ____cacheline_aligned_in_smp;
 	/* For user-space producer ring buffers, an atomic_t busy bit is used
 	 * to synchronize access to the ring buffers in the kernel, rather than
@@ -73,6 +74,7 @@ struct bpf_ringbuf {
 	unsigned long consumer_pos __aligned(PAGE_SIZE);
 	unsigned long producer_pos __aligned(PAGE_SIZE);
 	unsigned long pending_pos;
+	unsigned long overwrite_pos; /* position after the last overwritten record */
 	char data[] __aligned(PAGE_SIZE);
 };
 
@@ -166,7 +168,7 @@ static void bpf_ringbuf_notify(struct irq_work *work)
  * considering that the maximum value of data_sz is (4GB - 1), there
  * will be no overflow, so just note the size limit in the comments.
  */
-static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
+static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node, bool overwrite_mode)
 {
 	struct bpf_ringbuf *rb;
 
@@ -183,17 +185,25 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
 	rb->consumer_pos = 0;
 	rb->producer_pos = 0;
 	rb->pending_pos = 0;
+	rb->overwrite_mode = overwrite_mode;
 
 	return rb;
 }
 
 static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr)
 {
+	bool overwrite_mode = false;
 	struct bpf_ringbuf_map *rb_map;
 
 	if (attr->map_flags & ~RINGBUF_CREATE_FLAG_MASK)
 		return ERR_PTR(-EINVAL);
 
+	if (attr->map_flags & BPF_F_RB_OVERWRITE) {
+		if (attr->map_type != BPF_MAP_TYPE_RINGBUF)
+			return ERR_PTR(-EINVAL);
+		overwrite_mode = true;
+	}
+
 	if (attr->key_size || attr->value_size ||
 	    !is_power_of_2(attr->max_entries) ||
 	    !PAGE_ALIGNED(attr->max_entries))
@@ -205,7 +215,7 @@ static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr)
 
 	bpf_map_init_from_attr(&rb_map->map, attr);
 
-	rb_map->rb = bpf_ringbuf_alloc(attr->max_entries, rb_map->map.numa_node);
+	rb_map->rb = bpf_ringbuf_alloc(attr->max_entries, rb_map->map.numa_node, overwrite_mode);
 	if (!rb_map->rb) {
 		bpf_map_area_free(rb_map);
 		return ERR_PTR(-ENOMEM);
@@ -295,13 +305,26 @@ static int ringbuf_map_mmap_user(struct bpf_map *map, struct vm_area_struct *vma
 	return remap_vmalloc_range(vma, rb_map->rb, vma->vm_pgoff + RINGBUF_PGOFF);
 }
 
+/*
+ * Return an estimate of the available data in the ring buffer.
+ * Note: the returned value can exceed the actual ring buffer size because the
+ * function is not synchronized with the producer. The producer acquires the
+ * ring buffer's spinlock, but this function does not.
+ */
 static unsigned long ringbuf_avail_data_sz(struct bpf_ringbuf *rb)
 {
-	unsigned long cons_pos, prod_pos;
+	unsigned long cons_pos, prod_pos, over_pos;
 
 	cons_pos = smp_load_acquire(&rb->consumer_pos);
-	prod_pos = smp_load_acquire(&rb->producer_pos);
-	return prod_pos - cons_pos;
+
+	if (unlikely(rb->overwrite_mode)) {
+		over_pos = smp_load_acquire(&rb->overwrite_pos);
+		prod_pos = smp_load_acquire(&rb->producer_pos);
+		return prod_pos - max(cons_pos, over_pos);
+	} else {
+		prod_pos = smp_load_acquire(&rb->producer_pos);
+		return prod_pos - cons_pos;
+	}
 }
 
 static u32 ringbuf_total_data_sz(const struct bpf_ringbuf *rb)
@@ -404,11 +427,43 @@ bpf_ringbuf_restore_from_rec(struct bpf_ringbuf_hdr *hdr)
 	return (void*)((addr & PAGE_MASK) - off);
 }
 
+static bool bpf_ringbuf_has_space(const struct bpf_ringbuf *rb,
+				  unsigned long new_prod_pos,
+				  unsigned long cons_pos,
+				  unsigned long pend_pos)
+{
+	/*
+	 * No space if oldest not yet committed record until the newest
+	 * record span more than (ringbuf_size - 1).
+	 */
+	if (new_prod_pos - pend_pos > rb->mask)
+		return false;
+
+	/* Ok, we have space in overwrite mode */
+	if (unlikely(rb->overwrite_mode))
+		return true;
+
+	/*
+	 * No space if producer position advances more than (ringbuf_size - 1)
+	 * ahead of consumer position when not in overwrite mode.
+	 */
+	if (new_prod_pos - cons_pos > rb->mask)
+		return false;
+
+	return true;
+}
+
+static u32 bpf_ringbuf_round_up_hdr_len(u32 hdr_len)
+{
+	hdr_len &= ~BPF_RINGBUF_DISCARD_BIT;
+	return round_up(hdr_len + BPF_RINGBUF_HDR_SZ, 8);
+}
+
 static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
 {
-	unsigned long cons_pos, prod_pos, new_prod_pos, pend_pos, flags;
+	unsigned long cons_pos, prod_pos, new_prod_pos, pend_pos, over_pos, flags;
 	struct bpf_ringbuf_hdr *hdr;
-	u32 len, pg_off, tmp_size, hdr_len;
+	u32 len, pg_off, hdr_len;
 
 	if (unlikely(size > RINGBUF_MAX_RECORD_SZ))
 		return NULL;
@@ -431,24 +486,43 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
 		hdr_len = READ_ONCE(hdr->len);
 		if (hdr_len & BPF_RINGBUF_BUSY_BIT)
 			break;
-		tmp_size = hdr_len & ~BPF_RINGBUF_DISCARD_BIT;
-		tmp_size = round_up(tmp_size + BPF_RINGBUF_HDR_SZ, 8);
-		pend_pos += tmp_size;
+		pend_pos += bpf_ringbuf_round_up_hdr_len(hdr_len);
 	}
 	rb->pending_pos = pend_pos;
 
-	/* check for out of ringbuf space:
-	 * - by ensuring producer position doesn't advance more than
-	 *   (ringbuf_size - 1) ahead
-	 * - by ensuring oldest not yet committed record until newest
-	 *   record does not span more than (ringbuf_size - 1)
-	 */
-	if (new_prod_pos - cons_pos > rb->mask ||
-	    new_prod_pos - pend_pos > rb->mask) {
+	if (!bpf_ringbuf_has_space(rb, new_prod_pos, cons_pos, pend_pos)) {
 		raw_res_spin_unlock_irqrestore(&rb->spinlock, flags);
 		return NULL;
 	}
 
+	/*
+	 * In overwrite mode, advance overwrite_pos when the ring buffer is full.
+	 * The key points are to stay on record boundaries and consume enough records
+	 * to fit the new one.
+	 */
+	if (unlikely(rb->overwrite_mode)) {
+		over_pos = rb->overwrite_pos;
+		while (new_prod_pos - over_pos > rb->mask) {
+			hdr = (void *)rb->data + (over_pos & rb->mask);
+			hdr_len = READ_ONCE(hdr->len);
+			/*
+			 * The bpf_ringbuf_has_space() check above ensures we won’t
+			 * step over a record currently being worked on by another
+			 * producer.
+			 */
+			over_pos += bpf_ringbuf_round_up_hdr_len(hdr_len);
+		}
+		/*
+		 * smp_store_release(&rb->producer_pos, new_prod_pos) at
+		 * the end of the function ensures that when consumer sees
+		 * the updated rb->producer_pos, it always sees the updated
+		 * rb->overwrite_pos, so when consumer reads overwrite_pos
+		 * after smp_load_acquire(r->producer_pos), the overwrite_pos
+		 * will always be valid.
+		 */
+		WRITE_ONCE(rb->overwrite_pos, over_pos);
+	}
+
 	hdr = (void *)rb->data + (prod_pos & rb->mask);
 	pg_off = bpf_ringbuf_rec_pg_off(rb, hdr);
 	hdr->len = size | BPF_RINGBUF_BUSY_BIT;
@@ -578,6 +652,8 @@ BPF_CALL_2(bpf_ringbuf_query, struct bpf_map *, map, u64, flags)
 		return smp_load_acquire(&rb->consumer_pos);
 	case BPF_RB_PROD_POS:
 		return smp_load_acquire(&rb->producer_pos);
+	case BPF_RB_OVERWRITE_POS:
+		return smp_load_acquire(&rb->overwrite_pos);
 	default:
 		return 0;
 	}