Re: [PATCH v5 11/21] virtio-net: Return an error when vhost cannot enable RSS

[Jason Wang]

On Tue, Oct 17, 2023 at 12:10 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>
> vhost requires eBPF for RSS. Even when eBPF is not available, virtio-net
> reported RSS availability, and raised a warning only after the
> guest requested RSS, and the guest could not know that RSS is not
> available.
>
> Check RSS availability during device realization and return an error
> if RSS is requested but not available. Assert RSS availability when
> the guest actually requests the feature.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>  ebpf/ebpf_rss.h      |   2 +-
>  ebpf/ebpf_rss-stub.c |   4 +-
>  ebpf/ebpf_rss.c      |  68 +++++++++-----------------
>  hw/net/virtio-net.c  | 114 +++++++++++++++++++++----------------------
>  4 files changed, 82 insertions(+), 106 deletions(-)
>
> diff --git a/ebpf/ebpf_rss.h b/ebpf/ebpf_rss.h
> index bf3f2572c7..1128173572 100644
> --- a/ebpf/ebpf_rss.h
> +++ b/ebpf/ebpf_rss.h
> @@ -36,7 +36,7 @@ bool ebpf_rss_is_loaded(struct EBPFRSSContext *ctx);
>
>  bool ebpf_rss_load(struct EBPFRSSContext *ctx);
>
> -bool ebpf_rss_set_all(struct EBPFRSSContext *ctx, struct EBPFRSSConfig 
> *config,
> +void ebpf_rss_set_all(struct EBPFRSSContext *ctx, struct EBPFRSSConfig 
> *config,
>                        uint16_t *indirections_table, uint8_t *toeplitz_key);
>
>  void ebpf_rss_unload(struct EBPFRSSContext *ctx);
> diff --git a/ebpf/ebpf_rss-stub.c b/ebpf/ebpf_rss-stub.c
> index e71e229190..525b358597 100644
> --- a/ebpf/ebpf_rss-stub.c
> +++ b/ebpf/ebpf_rss-stub.c
> @@ -28,10 +28,10 @@ bool ebpf_rss_load(struct EBPFRSSContext *ctx)
>      return false;
>  }
>
> -bool ebpf_rss_set_all(struct EBPFRSSContext *ctx, struct EBPFRSSConfig 
> *config,
> +void ebpf_rss_set_all(struct EBPFRSSContext *ctx, struct EBPFRSSConfig 
> *config,
>                        uint16_t *indirections_table, uint8_t *toeplitz_key)
>  {
> -    return false;
> +    g_assert_not_reached();
>  }
>
>  void ebpf_rss_unload(struct EBPFRSSContext *ctx)
> diff --git a/ebpf/ebpf_rss.c b/ebpf/ebpf_rss.c
> index cee658c158..6cdf82d059 100644
> --- a/ebpf/ebpf_rss.c
> +++ b/ebpf/ebpf_rss.c
> @@ -74,42 +74,32 @@ error:
>      return false;
>  }
>
> -static bool ebpf_rss_set_config(struct EBPFRSSContext *ctx,
> +static void 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;
> -    }
> -    return true;
> +    assert(ebpf_rss_is_loaded(ctx));
> +    assert(!bpf_map_update_elem(ctx->map_configuration, &map_key, config, 
> 0));

Guest trigger-rable assertion should be avoided as much as possible.

Thanks