Re: [PATCH] Updating the GEM MAC IP to properly filter out the multicast addresses

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Thu, Nov 28, 2019 at 03:10:16PM +0000, Wasim, Bilal wrote:
> [PATCH] Updating the GEM MAC IP to properly filter out the multicast
> addresses. The current code makes a bad assumption that the most-significant
> byte of the MAC address is used to determine if the address is multicast or
> unicast, but in reality only a single bit is used to determine this. This
> caused IPv6 to not work.. Fix is now in place and has been tested with
> ZCU102-A53 / IPv6 on a TAP interface. Works well..

Hi Bilal,

The fix looks right to me but I have a few comments.

* Your patch seems a little wrongly formated.
[PATCH] goes into the Subject line for example and you're missing
path prefixes.

Do a git log -- hw/net/cadence_gem.c to see examples on how it should look.

* The patch will probably not pass checkpatch since you seem to have
long lines.

* We also need to update gem_receive_updatestats() to use the corrected macros.

More inline:

> 
> Signed-off-by: Bilal Wasim <bilal_wasim@mentor.com>
> ---
> hw/net/cadence_gem.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/net/cadence_gem.c b/hw/net/cadence_gem.c
> index b8be73d..f8bcbb3 100644
> --- a/hw/net/cadence_gem.c
> +++ b/hw/net/cadence_gem.c
> @@ -315,6 +315,12 @@
>  #define GEM_MODID_VALUE 0x00020118
> +/* IEEE has specified that the most significant bit of the most significant byte be used for
> + * distinguishing between Unicast and Multicast addresses.
> + * If its a 1, that means multicast, 0 means unicast.   */
> +#define IS_MULTICAST(address)           (((address[0] & 0x01) == 0x01) ? 1 : 0)



This can be simplified:
#define IS_MULTICAST(address) (address[0] & 1)

Actually, looking closer, we already have functions to do these checks in:
include/net/eth.h

static inline int is_multicast_ether_addr(const uint8_t *addr)
static inline int is_broadcast_ether_addr(const uint8_t *addr)
static inline int is_unicast_ether_addr(const uint8_t *addr)



> +#define IS_UNICAST(address)             (!IS_MULTICAST(address))
> +
> static inline uint64_t tx_desc_get_buffer(CadenceGEMState *s, uint32_t *desc)
> {
>      uint64_t ret = desc[0];
> @@ -690,21 +696,21 @@ static int gem_mac_address_filter(CadenceGEMState *s, const uint8_t *packet)
>      }
>      /* Accept packets -w- hash match? */
> -    if ((packet[0] == 0x01 && (s->regs[GEM_NWCFG] & GEM_NWCFG_MCAST_HASH)) ||
> -        (packet[0] != 0x01 && (s->regs[GEM_NWCFG] & GEM_NWCFG_UCAST_HASH))) {
> +    if ((IS_MULTICAST(packet) && (s->regs[GEM_NWCFG] & GEM_NWCFG_MCAST_HASH)) ||
> +        (IS_UNICAST(packet)   && (s->regs[GEM_NWCFG] & GEM_NWCFG_UCAST_HASH))) {
>          unsigned hash_index;
>          hash_index = calc_mac_hash(packet);
>          if (hash_index < 32) {
>              if (s->regs[GEM_HASHLO] & (1<<hash_index)) {
> -                return packet[0] == 0x01 ? GEM_RX_MULTICAST_HASH_ACCEPT :
> -                                           GEM_RX_UNICAST_HASH_ACCEPT;
> +                return IS_MULTICAST(packet) ? GEM_RX_MULTICAST_HASH_ACCEPT :
> +                                              GEM_RX_UNICAST_HASH_ACCEPT;
>              }
>          } else {
>              hash_index -= 32;
>              if (s->regs[GEM_HASHHI] & (1<<hash_index)) {
> -                return packet[0] == 0x01 ? GEM_RX_MULTICAST_HASH_ACCEPT :
> -                                           GEM_RX_UNICAST_HASH_ACCEPT;
> +                return IS_MULTICAST(packet) ? GEM_RX_MULTICAST_HASH_ACCEPT :
> +                                              GEM_RX_UNICAST_HASH_ACCEPT;
>              }
>          }
>      }
> --
> 2.9.3
>