Re: [PATCH v2] ethdev: document RSS default key and types

[Ophir Munk <ophirmu@mellanox.com>]

> -----Original Message-----
> From: Yongseok Koh
> Sent: Friday, November 09, 2018 1:07 AM
> To: Ophir Munk <ophirmu@mellanox.com>; Adrien Mazarguil
> <adrien.mazarguil@6wind.com>; Andrew Rybchenko
> <arybchenko@solarflare.com>
> Cc: Ferruh Yigit <ferruh.yigit@intel.com>; dev@dpdk.org; Thomas Monjalon
> <thomas@monjalon.net>; Asaf Penso <asafp@mellanox.com>; Shahaf
> Shuler <shahafs@mellanox.com>; Olga Shern <olgas@mellanox.com>
> Subject: Re: [dpdk-dev] [PATCH v2] ethdev: document RSS default key and
> types
> 
> 
> > On Nov 8, 2018, at 12:50 AM, Ophir Munk <ophirmu@mellanox.com>
> wrote:
> >
> >
> >
> >> -----Original Message-----
> >> From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
> >> Sent: Wednesday, November 07, 2018 6:41 PM
> >> To: Ophir Munk <ophirmu@mellanox.com>
> >> Cc: Ferruh Yigit <ferruh.yigit@intel.com>; Andrew Rybchenko
> >> <arybchenko@solarflare.com>; dev@dpdk.org; Thomas Monjalon
> >> <thomas@monjalon.net>; Asaf Penso <asafp@mellanox.com>; Shahaf
> Shuler
> >> <shahafs@mellanox.com>; Olga Shern <olgas@mellanox.com>
> >> Subject: Re: [dpdk-dev] [PATCH v2] ethdev: document RSS default key
> >> and types
> >>
> >> On Wed, Nov 07, 2018 at 03:13:07PM +0000, Ophir Munk wrote:
> >>>
> >>>> -----Original Message-----
> >>>> From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
> >>>> Sent: Wednesday, November 07, 2018 4:06 PM
> >>>> To: Ophir Munk <ophirmu@mellanox.com>
> >>>> Cc: Ferruh Yigit <ferruh.yigit@intel.com>; Andrew Rybchenko
> >>>> <arybchenko@solarflare.com>; dev@dpdk.org; Thomas Monjalon
> >>>> <thomas@monjalon.net>; Asaf Penso <asafp@mellanox.com>; Shahaf
> >>>> Shuler <shahafs@mellanox.com>; Olga Shern <olgas@mellanox.com>
> >>>> Subject: Re: [dpdk-dev] [PATCH v2] ethdev: document RSS default key
> >>>> and types
> >>>>
> >>>> On Wed, Nov 07, 2018 at 12:39:24PM +0000, Ophir Munk wrote:
> >>>>>> -----Original Message-----
> >>>>>> From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
> >>>>>> Sent: Wednesday, November 07, 2018 11:31 AM
> >>>>>> To: Ophir Munk <ophirmu@mellanox.com>
> >>>>>> Cc: Ferruh Yigit <ferruh.yigit@intel.com>; Andrew Rybchenko
> >>>>>> <arybchenko@solarflare.com>; dev@dpdk.org; Thomas Monjalon
> >>>>>> <thomas@monjalon.net>; Asaf Penso <asafp@mellanox.com>;
> >> Shahaf
> >>>>>> Shuler <shahafs@mellanox.com>; Olga Shern
> >> <olgas@mellanox.com>
> >>>>>> Subject: Re: [dpdk-dev] [PATCH v2] ethdev: document RSS default
> >>>>>> key and types
> >>>>>>
> >>>>>> On Wed, Nov 07, 2018 at 09:23:42AM +0000, Ophir Munk wrote:
> >>>>>>> struct rte_flow_action_rss include fields 'key' and 'types'.
> >>>>>>> Field 'key' is a pointer to bytes array (uint8_t *) which
> >>>>>>> contains the specific RSS hash key.
> >>>>>>> If an application is only interested in default RSS operation it
> >>>>>>> should not care about the specific hash key. The application can
> >>>>>>> set the hash key to NULL such that any PMD uses its
> >> default RSS key.
> >>>>>>>
> >>>>>>> Field 'types' is a uint64_t bits flag used to specify a specific
> >>>>>>> RSS hash type such as ETH_RSS_IP (see ETH_RSS_*).
> >>>>>>> If an application does not care about the specific RSS type it
> >>>>>>> can set this field to 0 such that any PMD uses its default type.
> >>>>>>>
> >>>>>>> Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
> >>>>>>> ---
> >>>>>>> lib/librte_ethdev/rte_flow.h | 9 +++++++--
> >>>>>>> 1 file changed, 7 insertions(+), 2 deletions(-)
> >>>>>>>
> >>>>>>> diff --git a/lib/librte_ethdev/rte_flow.h
> >>>>>>> b/lib/librte_ethdev/rte_flow.h index c0fe879..ca9e135 100644
> >>>>>>> --- a/lib/librte_ethdev/rte_flow.h
> >>>>>>> +++ b/lib/librte_ethdev/rte_flow.h
> >>>>>>> @@ -1782,10 +1782,15 @@ struct rte_flow_action_rss {
> >>>>>>> 	 * through.
> >>>>>>> 	 */
> >>>>>>> 	uint32_t level;
> >>>>>>> -	uint64_t types; /**< Specific RSS hash types (see
> >> ETH_RSS_*). */
> >>>>>>> +	/**
> >>>>>>> +	 * Specific RSS hash types (see ETH_RSS_*),
> >>>>>>> +	 * or 0 for PMD specific default.
> >>>>>>> +	 */
> >>>>>>> +	uint64_t types;
> >>>>>>> 	uint32_t key_len; /**< Hash key length in bytes. */
> >>>>>>> 	uint32_t queue_num; /**< Number of entries in @p queue.
> >> */
> >>>>>>> -	const uint8_t *key; /**< Hash key. */
> >>>>>>> +	/** Hash key, or NULL for PMD specific default key. */
> >>>>>>> +	const uint8_t *key;
> >>>>>>
> >>>>>> I'd suggest to document that on key_len instead. If key_len is
> >>>>>> nonzero, key cannot be NULL anyway.
> >>>>>
> >>>>> The decision if a key/len combination is valid is done in the PMD
> >>>>> action
> >>>> validation API.
> >>>>> For example, in MLX5 key==NULL and key_len==40 is accepted.
> >>>>> The combination key==NULL and key_len==0 should always succeeds,
> >>>> however the "must" parameter for RSS default is key==NULL and not
> >>>> key_len==0.
> >>>>
> >>>> I understand this is how the mlx5 PMD implemented it, but my point
> >>>> is that it makes more sense API-wise to define key_len == 0 as the
> >>>> trigger for a default RSS hash key than key == NULL.
> >>>>
> >>>> My suggestion is to follow the same trend as memcpy(), mmap(),
> >>>> snprintf() and other well-known functions that take a size when
> >>>> dealing with NULL/undefined pointers. Only size matters! :)
> >>>>
> >>>
> >>> Please let's stay backward compatible and consistent with previous
> >>> dpdk releases where key==NULL is used in struct rte_eth_rss_conf
> >>> (see
> >> code snippet in [1]).
> >>
> >> And I thought I wouldn't hear again from that structure after
> >> ac8d22de2394
> >> ("ethdev: flatten RSS configuration in flow API") got rid of it in
> >> rte_flow
> >> :)
> >>
> >> There is no need to be backward compatible with it particularly if
> >> doing so improves consistency (assuming you agree it does).
> >>
> >> Take "rss_hf" versus "types" fields for instance [2]. Unsetting the
> >> former disables RSS completely while unsetting the latter provides
> >> default RSS settings for that flow rule, simply because a RSS action
> >> that doesn't do RSS makes no sense (one could provide a single queue for
> that).
> >>
> >> Regarding "key_len", have a look at this other message [3] in the
> >> same thread which clearly states that i40e expects a zero key length
> >> to trigger default RSS, it doesn't rely on a NULL pointer.
> >>
> >> Generally speaking, I'm pushing for zero values in action objects to
> >> result in a safe default behavior. A nonzero key_len with a NULL key
> >> may result in a crash, while the reverse is inherently safer since
> >> one doesn't even need to check the size or pointer validity, e.g.:
> >>
> >> memcpy(target_device_rss_stuff, rss_conf->key, rss_conf->key_len);
> >>
> >> What's not to like?
> >>
> >
> > Some think key==NULL && key_len!=0 is senseless while other think
> key!=NULL && key_len==0 is senseless.
> > Let's agree on both key==NULL && key_len==0.
> 
> A bug's already been found by our QA team. The following command
> crashes.
>   flow create 0 ingress pattern eth / ipv6 / udp / end actions rss queues 0 end
> level 2 types udp end key_len 40 / end
> 
> due to null pointer access in the following code:
> 
> lib/librte_ethdev/rte_flow.c
> @@ -464,7 +464,7 @@ rte_flow_conv_action_conf(void *buf, const size_t
> size,
>                            }),
>                            size > sizeof(*dst.rss) ? sizeof(*dst.rss) : size);
>                 off = sizeof(*dst.rss);
>                 if (src.rss->key_len) {
>                         off = RTE_ALIGN_CEIL(off, sizeof(*dst.rss->key));
>                         tmp = sizeof(*src.rss->key) * src.rss->key_len;
>                         if (size >= off + tmp)
>                                 dst.rss->key = rte_memcpy
>                                         ((void *)((uintptr_t)dst.rss + off),
>                                          src.rss->key, tmp);
>                         off += tmp;
>                 }
> 
> 
> I wanted to submit a patch to add a sanity check,
> 
> -               if (src.rss->key_len) {
> +               if (src.rss->key && src.rss->key_len) {
> 
> but looks like we should conclude this thread first?
> Or, does the fix make any sense regardless of having key_len=0 or key=null
> for default key?
> Having more sanity check is no harm usually...
> 
> 
> Thanks,
> Yongseok
> 

The setfault is the result of commit a4391f8bae ("app/testpmd: set default RSS key as null").
Reverting this commit should fix the segfault but it also means there is no way to set default key (key=NULL) with testpmd.
Need to check if this is only a testpmd limitation and not all applications limitation.

We should decide how an application can set default RSS without knowing anything about keys.

> 
> >
> >> [2] "Re: [PATCH v2 07/15] ethdev: flatten RSS configuration in flow API"
> >>
> >>
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fma
> >> i
> >> ls.dpdk.org%2Farchives%2Fdev%2F2018-
> >>
> April%2F096235.html&amp;data=02%7C01%7Cophirmu%40mellanox.com%
> >>
> 7C4fdd2e5a838047c152c408d644cfe439%7Ca652971c7d2e4d9ba6a4d14925
> >>
> 6f461b%7C0%7C0%7C636772057013784575&amp;sdata=6JsomMO68lJoiNd
> >> ehRaNdn2xG9BSAgqCjxwpJJJOP8A%3D&amp;reserved=0
> >>
> >> [3] "Re: [dpdk-dev] [PATCH v6 07/16] ethdev: flatten RSS configuration in
> >>    flow API"
> >>
> >>
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fma
> >> i
> >> ls.dpdk.org%2Farchives%2Fdev%2F2018-
> >>
> May%2F100128.html&amp;data=02%7C01%7Cophirmu%40mellanox.com%7
> >>
> C4fdd2e5a838047c152c408d644cfe439%7Ca652971c7d2e4d9ba6a4d149256
> >>
> f461b%7C0%7C0%7C636772057013784575&amp;sdata=TXDTKLho8qyKlH%2
> >> FqBturGHWhvdfaACuMoqvl0eOjfcU%3D&amp;reserved=0
> >>
> >>> We should avoid confusing applications with setting key==NULL with
> >> legacy RSS and key_len==0 with rte_flows.
> >>>
> >>> With regard to trends APIs - I was thinking about free() where a
> >>> NULL pointer is acceptable :)
> >>
> >> Yeah, though free() doesn't take a size. On the other hand the
> >> behavior of
> >> realloc() is much more interesting when faced with a zero size :)
> >> That's probably one of the few exceptions so I guess my point still stands.
> >>
> >>>
> >>> [1]
> >>> File lib/librte_ethdev/rte_ethdev.h:
> >>>
> >>> /**
> >>> * A structure used to configure the Receive Side Scaling (RSS)
> >>> feature
> >>> * of an Ethernet port.
> >>> * If not NULL, the *rss_key* pointer of the *rss_conf* structure
> >>> points
> >>> * to an array holding the RSS key to use for hashing specific header
> >>> * fields of received packets. The length of this array should be
> >>> indicated
> >>> * by *rss_key_len* below. Otherwise, a default random hash key is
> >>> used by
> >>> * the device driver.
> >>> *
> >>> * The *rss_key_len* field of the *rss_conf* structure indicates the
> >>> length
> >>> * in bytes of the array pointed by *rss_key*. To be compatible, this
> >>> length
> >>> * will be checked in i40e only. Others assume 40 bytes to be used as
> >> before.
> >>> *
> >>> * ..........
> >>> */
> >>> struct rte_eth_rss_conf {
> >>> 	uint8_t *rss_key;    /**< If not NULL, 40-byte hash key. */
> >>> 	uint8_t rss_key_len; /**< hash key length in bytes. */
> >>> 	uint64_t rss_hf;     /**< Hash functions to apply - see below. */
> >>> };
> >>
> >> --
> >> Adrien Mazarguil
> >> 6WIND