linux-kernel - Re: [PATCH v4 1/2] crypto: engine

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Date:   Tue, 17 Mar 2020 13:08:18 +0000
From:   Iuliana Prodan <iuliana.prodan@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
CC:     Baolin Wang <baolin.wang@...aro.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        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: [PATCH v4 1/2] crypto: engine - support for parallel requests

On 3/17/2020 5:29 AM, Herbert Xu wrote:
> On Thu, Mar 12, 2020 at 12:45:54PM +0000, Iuliana Prodan wrote:
>>
>> There are two aspects here:
>> - if all requests go through crypto-engine, and, in this case, if there
>> is no space in hw queue, do_one_req returns 0, and actually there will
>> be no case of do_one_request() < 0;
> 
> OK, that makes sense.  However, this way of signaling for more
> requests can be racy.  Unless you can guarantee that the driver
> is not taking any requests from another engine queue (or any
> other source), just because it returned a positive value now does
> not mean that it would be able to take a request the next time
> you come around the loop.
> 

This case can happen right now, also. I can't guarantee that all drivers 
send all requests via crypto-engine.
This is the second aspect from my other mail. There are cases, when we 
send requests (non crypto API) to hardware without passing to crypto-engine.

To solve this, I'm thinking of adding new patches that doesn't do 
request dequeue from crypto-engine queue, just peek, and dequeues the 
request after was successfully executed by hardware (if it has 
MAY_BACKLOG flag, otherwise will dequeue it). What do you think?

Also, the above modification will imply changes in the drivers that use 
crypto-engine.

Thanks,
Iulia

>> I've tried this, but it implies modifications in all drivers. For
>> example, a driver, in case of error, it frees the resources of the
>> request. So, will need to map again a request.
> 
> I think what we are doing here is a major overhaul to the crypto
> engine API so while it's always a good idea to minimise the impact,
> we should not let the existing drivers constrain us too much.
> 
> Thanks,
>