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libbpf, xsk: Add libbpf_smp_store_release libbpf_smp_load_acquire 

Now that the AF_XDP rings have load-acquire/store-release semantics,
move libbpf to that as well.

The library-internal libbpf_smp_{load_acquire,store_release} are only
valid for 32-bit words on ARM64.

Also, remove the barriers that are no longer in use.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210305094113.413544-3-bjorn.topel@gmail.com
This commit is contained in:
Björn Töpel 2021-03-05 10:41:13 +01:00 committed by Andrii Nakryiko
parent a23b3f5697
commit 291471dd15
2 changed files with 55 additions and 34 deletions
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72
tools/lib/bpf/libbpf_util.h
View File

@ -5,6 +5,7 @@
#define __LIBBPF_LIBBPF_UTIL_H
#include <stdbool.h>
#include <linux/compiler.h>
#ifdef __cplusplus
extern "C" {
@ -15,29 +16,56 @@ extern "C" {
* application that uses libbpf.
*/
#if defined(__i386__) || defined(__x86_64__)
# define libbpf_smp_rmb() asm volatile("" : : : "memory")
# define libbpf_smp_wmb() asm volatile("" : : : "memory")
# define libbpf_smp_mb() \
asm volatile("lock; addl $0,-4(%%rsp)" : : : "memory", "cc")
/* Hinders stores to be observed before older loads. */
# define libbpf_smp_rwmb() asm volatile("" : : : "memory")
# define libbpf_smp_store_release(p, v) \
do { \
asm volatile("" : : : "memory"); \
WRITE_ONCE(*p, v); \
} while (0)
# define libbpf_smp_load_acquire(p) \
({ \
typeof(*p) ___p1 = READ_ONCE(*p); \
asm volatile("" : : : "memory"); \
___p1; \
})
#elif defined(__aarch64__)
# define libbpf_smp_rmb() asm volatile("dmb ishld" : : : "memory")
# define libbpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")
# define libbpf_smp_mb() asm volatile("dmb ish" : : : "memory")
# define libbpf_smp_rwmb() libbpf_smp_mb()
#elif defined(__arm__)
/* These are only valid for armv7 and above */
# define libbpf_smp_rmb() asm volatile("dmb ish" : : : "memory")
# define libbpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")
# define libbpf_smp_mb() asm volatile("dmb ish" : : : "memory")
# define libbpf_smp_rwmb() libbpf_smp_mb()
#else
/* Architecture missing native barrier functions. */
# define libbpf_smp_rmb() __sync_synchronize()
# define libbpf_smp_wmb() __sync_synchronize()
# define libbpf_smp_mb() __sync_synchronize()
# define libbpf_smp_rwmb() __sync_synchronize()
# define libbpf_smp_store_release(p, v) \
asm volatile ("stlr %w1, %0" : "=Q" (*p) : "r" (v) : "memory")
# define libbpf_smp_load_acquire(p) \
({ \
typeof(*p) ___p1; \
asm volatile ("ldar %w0, %1" \
: "=r" (___p1) : "Q" (*p) : "memory"); \
__p1; \
})
#elif defined(__riscv)
# define libbpf_smp_store_release(p, v) \
do { \
asm volatile ("fence rw,w" : : : "memory"); \
WRITE_ONCE(*p, v); \
} while (0)
# define libbpf_smp_load_acquire(p) \
({ \
typeof(*p) ___p1 = READ_ONCE(*p); \
asm volatile ("fence r,rw" : : : "memory"); \
___p1; \
})
#endif
#ifndef libbpf_smp_store_release
#define libbpf_smp_store_release(p, v) \
do { \
__sync_synchronize(); \
WRITE_ONCE(*p, v); \
} while (0)
#endif
#ifndef libbpf_smp_load_acquire
#define libbpf_smp_load_acquire(p) \
({ \
typeof(*p) ___p1 = READ_ONCE(*p); \
__sync_synchronize(); \
___p1; \
})
#endif
#ifdef __cplusplus

17
tools/lib/bpf/xsk.h
View File

@ -96,7 +96,8 @@ static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
* this function. Without this optimization it whould have been
* free_entries = r->cached_prod - r->cached_cons + r->size.
*/
r->cached_cons = *r->consumer + r->size;
r->cached_cons = libbpf_smp_load_acquire(r->consumer);
r->cached_cons += r->size;
return r->cached_cons - r->cached_prod;
}
@ -106,7 +107,7 @@ static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
__u32 entries = r->cached_prod - r->cached_cons;
if (entries == 0) {
r->cached_prod = *r->producer;
r->cached_prod = libbpf_smp_load_acquire(r->producer);
entries = r->cached_prod - r->cached_cons;
}
@ -129,9 +130,7 @@ static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, __u32 nb)
/* Make sure everything has been written to the ring before indicating
* this to the kernel by writing the producer pointer.
*/
libbpf_smp_wmb();
*prod->producer += nb;
libbpf_smp_store_release(prod->producer, *prod->producer + nb);
}
static inline __u32 xsk_ring_cons__peek(struct xsk_ring_cons *cons, __u32 nb, __u32 *idx)
@ -139,11 +138,6 @@ static inline __u32 xsk_ring_cons__peek(struct xsk_ring_cons *cons, __u32 nb, __
__u32 entries = xsk_cons_nb_avail(cons, nb);
if (entries > 0) {
/* Make sure we do not speculatively read the data before
* we have received the packet buffers from the ring.
*/
libbpf_smp_rmb();
*idx = cons->cached_cons;
cons->cached_cons += entries;
}
@ -161,9 +155,8 @@ static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, __u32 nb)
/* Make sure data has been read before indicating we are done
* with the entries by updating the consumer pointer.
*/
libbpf_smp_rwmb();
libbpf_smp_store_release(cons->consumer, *cons->consumer + nb);
*cons->consumer += nb;
}
static inline void *xsk_umem__get_data(void *umem_area, __u64 addr)