linux-kernel - Re: [RFC PATCH] Crypto-engine support for parallel requests

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Date:   Wed, 22 Jan 2020 12:29:22 +0000
From:   Iuliana Prodan <iuliana.prodan@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        Baolin Wang <baolin.wang@...aro.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>
CC:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Horia Geanta <horia.geanta@....com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Maxime Ripard <mripard@...nel.org>,
        Aymen Sghaier <aymen.sghaier@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Silvano Di Ninno <silvano.dininno@....com>,
        Franck Lenormand <franck.lenormand@....com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [RFC PATCH] Crypto-engine support for parallel requests

On 1/22/2020 12:41 PM, Corentin Labbe wrote:
> On Tue, Jan 21, 2020 at 02:20:27PM +0000, Iuliana Prodan wrote:
>> On 1/21/2020 12:00 PM, Corentin Labbe wrote:
>>> On Tue, Jan 21, 2020 at 01:32:29AM +0200, Iuliana Prodan wrote:
>>>> Added support for executing multiple requests, in parallel,
>>>> for crypto engine.
>>>> A no_reqs is initialized and set in the new
>>>> crypto_engine_alloc_init_and_set function.
>>>> 
>>>>
>>>
>>> Hello
>>>
>>> In your model, who is running finalize_request() ?
>> finalize_request() in CAAM, and in other drivers, is called on the _done
>> callback (stm32, virtio and omap).
>>
>>> In caam it seems that you have a taskqueue dedicated for that but you cannot assume that all drivers will have this.
>>> I think the crypto_engine should be sufficient by itself and does not need external thread/taskqueue.
>>>
>>> But in your case, it seems that you dont have the choice, since do_one_request does not "do" but simply enqueue the request in the "jobring".
>>>
>> But, do_one_request it shouldn't, necessary,  execute the request. Is ok
>> to enqueue it, since we have asynchronous requests. do_one_request is
>> not blocking.
>>
>>> What about adding along prepare/do_one_request/unprepare a new enqueue()/can_do_more() function ?
>>>
>>> The stream will be:
>>> retry:
>>> optionnal prepare
>>> optionnal enqueue
>>> optionnal can_do_more() (goto retry)
>>> optionnal do_one_request
>>>
>>> then
>>> finalize()
>>> optionnal unprepare
>>>
>>
>> I'm planning to improve crypto-engine incrementally, so I'm taking one
>> step at a time :)
>> But I'm not sure if adding an enqueue operation is a good idea, since,
>> my understanding, is that do_one_request is a non-blocking operation and
>> it shouldn't execute the request.
> 
> do_one_request is a blocking operation on amlogic/sun8i-ce/sun8i-ss and the "documentation" is clear "@do_one_request: do encryption for current request".
> But I agree that is a bit small for a documentation.
> 

Herbert, Baolin,

What do you think about do_one_requet operation: is blocking or not?

There are several drivers (stm32, omap, virtio, caam) that include 
crypto-engine, and uses do_one_request as non-blocking, only the ones 
mentioned and implemented by Corentin use do_one_request as blocking.

>>
>> IMO, the crypto-engine flow should be kept simple:
>> 1. a request comes to hw -> this is doing transfer_request_to_engine;
>> 2. CE enqueue the requests
>> 3. on pump_requests:
>> 	3. a) optional prepare operation
>> 	3. b) sends the reqs to hw, by do_one_request operation. To wait for
>> completion here it contradicts the asynchronous crypto API.
> 
> There are no contradiction, the call is asynchronous for the user of the API.
> 
>> do_one_request operation has a crypto_async_request type as argument.
>> Note: Step 3. b) can be done several times, depending on size of hw queue.
>> 4. in driver, when req is done:
>> 	4. a) optional unprepare operation
>> 	4. b) crypto_finalize_request is called
>> 	
> 
> Since Herbert say the same thing than me:
> "Instead, we should just let the driver tell us when it is ready to accept more requests."
> Let me insist on my proposal, I have updated my serie, and it should handle your case and mine.
> I will send it within minutes.
> 

Corentin,

In your new proposal, a few patches include my modifications. The others 
include a solution that fits your drivers very well, but implies 
modifications in all the other 4 drivers. It's not backwards compatible.
I believe it can be done better, so we won't need to modify, _at all_, 
the other drivers.

I'm working on a new version for my RFC, that has the can_enqueue_more, 
as Herbert suggested, but I would really want to know how 
crypto-engine's do_one_request was thought: blocking or non-blocking?

Just your driver(s) use it as blocking, the other examples use it to 
enqueue (don't block in waiting for request to finish).

Thanks,
Iulia