To prepare for supporting boot-time page size selection, refactor code to remove assumptions about PAGE_SIZE being compile-time constant. Code intended to be equivalent when compile-time page size is active. Refactor "struct bpf_ringbuf" so that consumer_pos, producer_pos, pending_pos and data are no longer embedded at (static) page offsets within the struct. This can't work for boot-time page size because the page size isn't known at compile-time. Instead, only define the meta data in the struct, along with pointers to those values. At "struct bpf_ringbuf" allocation time, the extra pages are allocated at the end and the pointers are initialized to point to the correct locations. Additionally, only expose the __PAGE_SIZE enum to BTF for compile-time page size builds. We don't know the page size at compile-time for boot-time builds. NOTE: This may need some extra thought; perhaps __PAGE_SIZE should be exposed as 0 in this case? And/or perhaps __PAGE_SIZE_MIN/__PAGE_SIZE_MAX should be exposed? And there would need to be a runtime mechanism for querying the page size (e.g. getpagesize()). Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> --- ***NOTE*** Any confused maintainers may want to read the cover note here for context: https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@xxxxxxx/ kernel/bpf/core.c | 9 ++++++-- kernel/bpf/ringbuf.c | 54 ++++++++++++++++++++++++-------------------- 2 files changed, 37 insertions(+), 26 deletions(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 7ee62e38faf0e..485875aa78e63 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -89,10 +89,15 @@ void *bpf_internal_load_pointer_neg_helper(const struct sk_buff *skb, int k, uns return NULL; } -/* tell bpf programs that include vmlinux.h kernel's PAGE_SIZE */ +/* + * tell bpf programs that include vmlinux.h kernel's PAGE_SIZE. We can only do + * this for compile-time PAGE_SIZE builds. + */ +#if PAGE_SIZE_MIN == PAGE_SIZE_MAX enum page_size_enum { __PAGE_SIZE = PAGE_SIZE }; +#endif struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flags) { @@ -100,7 +105,7 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag struct bpf_prog_aux *aux; struct bpf_prog *fp; - size = round_up(size, __PAGE_SIZE); + size = round_up(size, PAGE_SIZE); fp = __vmalloc(size, gfp_flags); if (fp == NULL) return NULL; diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c index e20b90c361316..8e4093ddbc638 100644 --- a/kernel/bpf/ringbuf.c +++ b/kernel/bpf/ringbuf.c @@ -14,9 +14,9 @@ #define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE) -/* non-mmap()'able part of bpf_ringbuf (everything up to consumer page) */ +/* non-mmap()'able part of bpf_ringbuf (everything defined in struct) */ #define RINGBUF_PGOFF \ - (offsetof(struct bpf_ringbuf, consumer_pos) >> PAGE_SHIFT) + (PAGE_ALIGN(sizeof(struct bpf_ringbuf)) >> PAGE_SHIFT) /* consumer page and producer page */ #define RINGBUF_POS_PAGES 2 #define RINGBUF_NR_META_PAGES (RINGBUF_PGOFF + RINGBUF_POS_PAGES) @@ -69,10 +69,10 @@ struct bpf_ringbuf { * validate each sample to ensure that they're correctly formatted, and * fully contained within the ring buffer. */ - unsigned long consumer_pos __aligned(PAGE_SIZE); - unsigned long producer_pos __aligned(PAGE_SIZE); - unsigned long pending_pos; - char data[] __aligned(PAGE_SIZE); + unsigned long *consumer_pos; + unsigned long *producer_pos; + unsigned long *pending_pos; + char *data; }; struct bpf_ringbuf_map { @@ -134,9 +134,15 @@ static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node) rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages, VM_MAP | VM_USERMAP, PAGE_KERNEL); if (rb) { + void *base = rb; + kmemleak_not_leak(pages); rb->pages = pages; rb->nr_pages = nr_pages; + rb->consumer_pos = (unsigned long *)(base + PAGE_SIZE * RINGBUF_PGOFF); + rb->producer_pos = (unsigned long *)(base + PAGE_SIZE * (RINGBUF_PGOFF + 1)); + rb->pending_pos = rb->producer_pos + 1; + rb->data = base + PAGE_SIZE * nr_meta_pages; return rb; } @@ -179,9 +185,9 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node) init_irq_work(&rb->work, bpf_ringbuf_notify); rb->mask = data_sz - 1; - rb->consumer_pos = 0; - rb->producer_pos = 0; - rb->pending_pos = 0; + *rb->consumer_pos = 0; + *rb->producer_pos = 0; + *rb->pending_pos = 0; return rb; } @@ -300,8 +306,8 @@ static unsigned long ringbuf_avail_data_sz(struct bpf_ringbuf *rb) { unsigned long cons_pos, prod_pos; - cons_pos = smp_load_acquire(&rb->consumer_pos); - prod_pos = smp_load_acquire(&rb->producer_pos); + cons_pos = smp_load_acquire(rb->consumer_pos); + prod_pos = smp_load_acquire(rb->producer_pos); return prod_pos - cons_pos; } @@ -418,7 +424,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size) if (len > ringbuf_total_data_sz(rb)) return NULL; - cons_pos = smp_load_acquire(&rb->consumer_pos); + cons_pos = smp_load_acquire(rb->consumer_pos); if (in_nmi()) { if (!spin_trylock_irqsave(&rb->spinlock, flags)) @@ -427,8 +433,8 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size) spin_lock_irqsave(&rb->spinlock, flags); } - pend_pos = rb->pending_pos; - prod_pos = rb->producer_pos; + pend_pos = *rb->pending_pos; + prod_pos = *rb->producer_pos; new_prod_pos = prod_pos + len; while (pend_pos < prod_pos) { @@ -440,7 +446,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size) tmp_size = round_up(tmp_size + BPF_RINGBUF_HDR_SZ, 8); pend_pos += tmp_size; } - rb->pending_pos = pend_pos; + *rb->pending_pos = pend_pos; /* check for out of ringbuf space: * - by ensuring producer position doesn't advance more than @@ -460,7 +466,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size) hdr->pg_off = pg_off; /* pairs with consumer's smp_load_acquire() */ - smp_store_release(&rb->producer_pos, new_prod_pos); + smp_store_release(rb->producer_pos, new_prod_pos); spin_unlock_irqrestore(&rb->spinlock, flags); @@ -506,7 +512,7 @@ static void bpf_ringbuf_commit(void *sample, u64 flags, bool discard) * new data availability */ rec_pos = (void *)hdr - (void *)rb->data; - cons_pos = smp_load_acquire(&rb->consumer_pos) & rb->mask; + cons_pos = smp_load_acquire(rb->consumer_pos) & rb->mask; if (flags & BPF_RB_FORCE_WAKEUP) irq_work_queue(&rb->work); @@ -580,9 +586,9 @@ BPF_CALL_2(bpf_ringbuf_query, struct bpf_map *, map, u64, flags) case BPF_RB_RING_SIZE: return ringbuf_total_data_sz(rb); case BPF_RB_CONS_POS: - return smp_load_acquire(&rb->consumer_pos); + return smp_load_acquire(rb->consumer_pos); case BPF_RB_PROD_POS: - return smp_load_acquire(&rb->producer_pos); + return smp_load_acquire(rb->producer_pos); default: return 0; } @@ -680,12 +686,12 @@ static int __bpf_user_ringbuf_peek(struct bpf_ringbuf *rb, void **sample, u32 *s u64 cons_pos, prod_pos; /* Synchronizes with smp_store_release() in user-space producer. */ - prod_pos = smp_load_acquire(&rb->producer_pos); + prod_pos = smp_load_acquire(rb->producer_pos); if (prod_pos % 8) return -EINVAL; /* Synchronizes with smp_store_release() in __bpf_user_ringbuf_sample_release() */ - cons_pos = smp_load_acquire(&rb->consumer_pos); + cons_pos = smp_load_acquire(rb->consumer_pos); if (cons_pos >= prod_pos) return -ENODATA; @@ -715,7 +721,7 @@ static int __bpf_user_ringbuf_peek(struct bpf_ringbuf *rb, void **sample, u32 *s * Update the consumer pos, and return -EAGAIN so the caller * knows to skip this sample and try to read the next one. */ - smp_store_release(&rb->consumer_pos, cons_pos + total_len); + smp_store_release(rb->consumer_pos, cons_pos + total_len); return -EAGAIN; } @@ -737,9 +743,9 @@ static void __bpf_user_ringbuf_sample_release(struct bpf_ringbuf *rb, size_t siz * prevents another task from writing to consumer_pos after it was read * by this task with smp_load_acquire() in __bpf_user_ringbuf_peek(). */ - consumer_pos = rb->consumer_pos; + consumer_pos = *rb->consumer_pos; /* Synchronizes with smp_load_acquire() in user-space producer. */ - smp_store_release(&rb->consumer_pos, consumer_pos + rounded_size); + smp_store_release(rb->consumer_pos, consumer_pos + rounded_size); } BPF_CALL_4(bpf_user_ringbuf_drain, struct bpf_map *, map, -- 2.43.0
