Re: [PATCH v5 1/5] ebpf: Added eBPF map update through mmap.

[Jason Wang <jasowang@redhat.com>]

On Thu, Aug 3, 2023 at 5:01 AM Andrew Melnychenko <andrew@daynix.com> wrote:
>
> Changed eBPF map updates through mmaped array.
> Mmaped arrays provide direct access to map data.
> It should omit using bpf_map_update_elem() call,
> which may require capabilities that are not present.
>
> Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
> ---
>  ebpf/ebpf_rss.c | 117 ++++++++++++++++++++++++++++++++++++++----------
>  ebpf/ebpf_rss.h |   5 +++
>  2 files changed, 99 insertions(+), 23 deletions(-)
>
> diff --git a/ebpf/ebpf_rss.c b/ebpf/ebpf_rss.c
> index cee658c158b..247f5eee1b6 100644
> --- a/ebpf/ebpf_rss.c
> +++ b/ebpf/ebpf_rss.c
> @@ -27,19 +27,83 @@ void ebpf_rss_init(struct EBPFRSSContext *ctx)
>  {
>      if (ctx != NULL) {
>          ctx->obj = NULL;
> +        ctx->program_fd = -1;
> +        ctx->map_configuration = -1;
> +        ctx->map_toeplitz_key = -1;
> +        ctx->map_indirections_table = -1;
> +
> +        ctx->mmap_configuration = NULL;
> +        ctx->mmap_toeplitz_key = NULL;
> +        ctx->mmap_indirections_table = NULL;
>      }
>  }
>
>  bool ebpf_rss_is_loaded(struct EBPFRSSContext *ctx)
>  {
> -    return ctx != NULL && ctx->obj != NULL;
> +    return ctx != NULL && (ctx->obj != NULL || ctx->program_fd != -1);
> +}
> +
> +static bool ebpf_rss_mmap(struct EBPFRSSContext *ctx)
> +{
> +    if (!ebpf_rss_is_loaded(ctx)) {
> +        return false;
> +    }
> +
> +    ctx->mmap_configuration = mmap(NULL, qemu_real_host_page_size(),
> +                                   PROT_READ | PROT_WRITE, MAP_SHARED,
> +                                   ctx->map_configuration, 0);
> +    if (ctx->mmap_configuration == MAP_FAILED) {
> +        trace_ebpf_error("eBPF RSS", "can not mmap eBPF configuration array");
> +        return false;
> +    }
> +    ctx->mmap_toeplitz_key = mmap(NULL, qemu_real_host_page_size(),
> +                                   PROT_READ | PROT_WRITE, MAP_SHARED,
> +                                   ctx->map_toeplitz_key, 0);
> +    if (ctx->mmap_toeplitz_key == MAP_FAILED) {
> +        trace_ebpf_error("eBPF RSS", "can not mmap eBPF toeplitz key");
> +        goto toeplitz_fail;
> +    }
> +    ctx->mmap_indirections_table = mmap(NULL, qemu_real_host_page_size(),
> +                                   PROT_READ | PROT_WRITE, MAP_SHARED,
> +                                   ctx->map_indirections_table, 0);
> +    if (ctx->mmap_indirections_table == MAP_FAILED) {
> +        trace_ebpf_error("eBPF RSS", "can not mmap eBPF indirection table");
> +        goto indirection_fail;
> +    }
> +
> +    return true;
> +
> +indirection_fail:
> +    munmap(ctx->mmap_toeplitz_key, qemu_real_host_page_size());
> +toeplitz_fail:
> +    munmap(ctx->mmap_configuration, qemu_real_host_page_size());
> +
> +    ctx->mmap_configuration = NULL;
> +    ctx->mmap_toeplitz_key = NULL;
> +    ctx->mmap_indirections_table = NULL;
> +    return false;
> +}
> +
> +static void ebpf_rss_munmap(struct EBPFRSSContext *ctx)
> +{
> +    if (!ebpf_rss_is_loaded(ctx)) {
> +        return;
> +    }
> +
> +    munmap(ctx->mmap_indirections_table, qemu_real_host_page_size());
> +    munmap(ctx->mmap_toeplitz_key, qemu_real_host_page_size());
> +    munmap(ctx->mmap_configuration, qemu_real_host_page_size());
> +
> +    ctx->mmap_configuration = NULL;
> +    ctx->mmap_toeplitz_key = NULL;
> +    ctx->mmap_indirections_table = NULL;
>  }
>
>  bool ebpf_rss_load(struct EBPFRSSContext *ctx)
>  {
>      struct rss_bpf *rss_bpf_ctx;
>
> -    if (ctx == NULL) {
> +    if (ctx == NULL || ebpf_rss_is_loaded(ctx)) {
>          return false;
>      }
>
> @@ -66,10 +130,18 @@ bool ebpf_rss_load(struct EBPFRSSContext *ctx)
>      ctx->map_toeplitz_key = bpf_map__fd(
>              rss_bpf_ctx->maps.tap_rss_map_toeplitz_key);
>
> +    if (!ebpf_rss_mmap(ctx)) {
> +        goto error;
> +    }
> +
>      return true;
>  error:
>      rss_bpf__destroy(rss_bpf_ctx);
>      ctx->obj = NULL;
> +    ctx->program_fd = -1;
> +    ctx->map_configuration = -1;
> +    ctx->map_toeplitz_key = -1;
> +    ctx->map_indirections_table = -1;
>
>      return false;
>  }
> @@ -77,15 +149,11 @@ error:
>  static bool ebpf_rss_set_config(struct EBPFRSSContext *ctx,
>                                  struct EBPFRSSConfig *config)
>  {
> -    uint32_t map_key = 0;
> -
>      if (!ebpf_rss_is_loaded(ctx)) {
>          return false;
>      }
> -    if (bpf_map_update_elem(ctx->map_configuration,
> -                            &map_key, config, 0) < 0) {
> -        return false;
> -    }
> +
> +    memcpy(ctx->mmap_configuration, config, sizeof(*config));
>      return true;
>  }
>
> @@ -93,27 +161,19 @@ static bool ebpf_rss_set_indirections_table(struct EBPFRSSContext *ctx,
>                                              uint16_t *indirections_table,
>                                              size_t len)
>  {
> -    uint32_t i = 0;
> -
>      if (!ebpf_rss_is_loaded(ctx) || indirections_table == NULL ||
>         len > VIRTIO_NET_RSS_MAX_TABLE_LEN) {
>          return false;
>      }
>
> -    for (; i < len; ++i) {
> -        if (bpf_map_update_elem(ctx->map_indirections_table, &i,
> -                                indirections_table + i, 0) < 0) {
> -            return false;
> -        }
> -    }
> +    memcpy(ctx->mmap_indirections_table, indirections_table,
> +            sizeof(*indirections_table) * len);

As discussed, should we stick the compatibility on the host without
bpf mmap support?

If we don't, we need at least probe BPF mmap and disable ebpf rss? If
yes, we should track if the map is mmaped and switch between memcpy
and syscall.

Thanks

>      return true;
>  }
>
>  static bool ebpf_rss_set_toepliz_key(struct EBPFRSSContext *ctx,
>                                       uint8_t *toeplitz_key)
>  {
> -    uint32_t map_key = 0;
> -
>      /* prepare toeplitz key */
>      uint8_t toe[VIRTIO_NET_RSS_MAX_KEY_SIZE] = {};
>
> @@ -123,10 +183,7 @@ static bool ebpf_rss_set_toepliz_key(struct EBPFRSSContext *ctx,
>      memcpy(toe, toeplitz_key, VIRTIO_NET_RSS_MAX_KEY_SIZE);
>      *(uint32_t *)toe = ntohl(*(uint32_t *)toe);
>
> -    if (bpf_map_update_elem(ctx->map_toeplitz_key, &map_key, toe,
> -                            0) < 0) {
> -        return false;
> -    }
> +    memcpy(ctx->mmap_toeplitz_key, toe, VIRTIO_NET_RSS_MAX_KEY_SIZE);
>      return true;
>  }
>
> @@ -160,6 +217,20 @@ void ebpf_rss_unload(struct EBPFRSSContext *ctx)
>          return;
>      }
>
> -    rss_bpf__destroy(ctx->obj);
> +    ebpf_rss_munmap(ctx);
> +
> +    if (ctx->obj) {
> +        rss_bpf__destroy(ctx->obj);
> +    } else {
> +        close(ctx->program_fd);
> +        close(ctx->map_configuration);
> +        close(ctx->map_toeplitz_key);
> +        close(ctx->map_indirections_table);
> +    }
> +
>      ctx->obj = NULL;
> +    ctx->program_fd = -1;
> +    ctx->map_configuration = -1;
> +    ctx->map_toeplitz_key = -1;
> +    ctx->map_indirections_table = -1;
>  }
> diff --git a/ebpf/ebpf_rss.h b/ebpf/ebpf_rss.h
> index bf3f2572c7c..ab08a7266d0 100644
> --- a/ebpf/ebpf_rss.h
> +++ b/ebpf/ebpf_rss.h
> @@ -20,6 +20,11 @@ struct EBPFRSSContext {
>      int map_configuration;
>      int map_toeplitz_key;
>      int map_indirections_table;
> +
> +    /* mapped eBPF maps for direct access to omit bpf_map_update_elem() */
> +    void *mmap_configuration;
> +    void *mmap_toeplitz_key;
> +    void *mmap_indirections_table;
>  };
>
>  struct EBPFRSSConfig {
> --
> 2.41.0
>