Re: [dpdk-dev] [PATCH v1 0/2] declare crypto asym xform immutable

[Shally Verma <shallyv@marvell.com>]

Hi Anoob

Seems your reply is not in plaintext which will make it difficult for inline response. So, please take care of that when you reply.
Rest, please see my response inline.

From: Anoob Joseph 
Sent: Thursday, July 25, 2019 9:46 AM
To: Ayuj Verma <ayverma@marvell.com>; akhil.goyal@nxp.com
Cc: arkadiuszx.kusztal@intel.com; Shally Verma <shallyv@marvell.com>; Sunila Sahu <ssahu@marvell.com>; Kanaka Durga Kotamarthy <kkotamarthy@marvell.com>; dev@dpdk.org; Fiona Trahe <fiona.trahe@intel.com>
Subject: RE: [PATCH v1 0/2] declare crypto asym xform immutable

Hi Ayuj,

I believe there are couple of issues with this patch.

Are these experimental APIs? I believe they were made stable this release and I'm not sure if it is a right practice to edit an API without deprecation notice after it is made stable. Especially now that RC2 is done. @Akhil, what is your take on this?
[Shally] These are experimental still, hence no deprecation notice. We checked about it with Fiona, Akhil before.

I think, the approach here is wrong. If the lifetime of the session is expected to be only few packets, then session-less (which I believe is in the pipeline) would make more sense. 
[Shally] See my response further below on this.

If the lifetime of the session is expected to be more than that, then having this feature/limitation would make application more complicated. Also, since one asymmetric session can hold both public & private keys, the implicit assumption would be, the session can be used for multiple kinds of operations. This change is in contradiction with that. 
[Shally] Why the contradiction here? There's no change in session usage from current version. Currently too, once keys are set on asymmetric session, they are used with multiple operations using that sessions, example - once RSA xform is set with keys, then one can perform sign/verify/enc/dec. So, I don't see any change in that notion with this proposal. All we are changing is, PMD which does not need to store keys in specific format (like openssl PMD), can just hold app buffer pointer till session-lifetime (eventually giving same effect as sessionless). It will help such PMDs to optimize their session setup time by avoiding unnecessary memcpy of keys buffers.

But my major concern is how this can lead to accidental errors. Making the argument as const will mean the API won't edit its contents. But if there is a pointer in that (key happens to be a pointer inside the xform), having const for xform will not help. This is my understanding. Please correct me if I'm wrong. 
[Shally] This spec says " xform and its buffers remain constant" . So, intention is to state to apps that buffer passed to xform should be const in nature and that they should not modify it.

Also, I could have the xform allocated from stack (non const, regular local variable) and then call the session_init. Would compiler throw an issue in that case? I doubt so.

void abc(const int t)
{
        printf("%d\n", t);
}

void main()
{
        int t = 0;
        abc(t);
        t = 2;
        abc(t);
}

To summarize, if this assumption is accepted, then compiler will not be able to ensure it. And to properly use it, application will have to be drafted differently. And when similar effect can be achieved by having session-less, this seems redundant.
[Shally]  Compiler may or may not warn on typecast error here. That's why spec and documentation are put in place to ensure that application don't reuse them or destroy them once "xform and its buffers" are set on session. And, same will need to be documented about xform for session-less usage as well.
Even there, we would ensure that application do not re-use or modify xform and its buffers until dequeue happen. So, practically I see, application would have to take of these cases in session-less as well.

Since in session-based case, xform are set on it than ops, so we're moving same definition on session. So for PMDs which support sessions-based implementations ( like ours) , believe it completely make sense to enable sessions to have sessionless effect.  If we don't change spec to enable optimization, then we're making 1-approach slower than other.  PMDs can adopt any approach more suitable to them. But spec could be made flexible to allow them to experiment with both approaches for performance. Else , PMDs will be forced to experiment around sessionless which may be eventually be an unnecessary overhead for them. 

Thanks
Shally

So this change is NACK from my side.

Thanks,
Anoob

From: Ayuj Verma 
Sent: Wednesday, July 24, 2019 2:23 PM
To: mailto:akhil.goyal@nxp.com
Cc: mailto:arkadiuszx.kusztal@intel.com; Shally Verma <mailto:shallyv@marvell.com>; Sunila Sahu <mailto:ssahu@marvell.com>; Kanaka Durga Kotamarthy <mailto:kkotamarthy@marvell.com>; Anoob Joseph <mailto:anoobj@marvell.com>; mailto:dev@dpdk.org; Fiona Trahe <mailto:fiona.trahe@intel.com>
Subject: Re: [PATCH v1 0/2] declare crypto asym xform immutable

+Fiona.
________________________________________
From: Ayuj Verma <mailto:ayverma@marvell.com>
Sent: 24 July 2019 14:21:55
To: mailto:akhil.goyal@nxp.com <mailto:akhil.goyal@nxp.com>
Cc: mailto:arkadiuszx.kusztal@intel.com <mailto:arkadiuszx.kusztal@intel.com>; Shally Verma <mailto:shallyv@marvell.com>; Sunila Sahu <mailto:ssahu@marvell.com>; Kanaka Durga Kotamarthy <mailto:kkotamarthy@marvell.com>; Anoob Joseph <mailto:anoobj@marvell.com>; mailto:dev@dpdk.org <mailto:dev@dpdk.org>; Ayuj Verma <mailto:ayverma@marvell.com>
Subject: [PATCH v1 0/2] declare crypto asym xform immutable 
 
Mark asym xform as immutable till lifetime
of session. It will save session setup time for
PMDs, which doesn't require any manipulation of
xform data, by directly using these buffers.

* Updated xform type in session init/configure
  API as constant.
* Updated doc with proper transform description.
* Updated openssl PMD with above changes.

Ayuj Verma (2):
  lib/crypto: declare crypto asym xform immutable
  crypto/openssl: mark asym xform constant

 doc/guides/prog_guide/cryptodev_lib.rst      | 10 ++++++++++
 drivers/crypto/openssl/rte_openssl_pmd_ops.c |  8 ++++----
 lib/librte_cryptodev/rte_cryptodev.c         |  2 +-
 lib/librte_cryptodev/rte_cryptodev.h         |  2 +-
 lib/librte_cryptodev/rte_cryptodev_pmd.h     |  2 +-
 5 files changed, 17 insertions(+), 7 deletions(-)

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