linux-kernel - Re: [RFC PATCH 0/4] crypto: add CRYPTO_TFM_REQ

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Date:   Wed, 25 Nov 2020 23:39:22 +0200
From:   Iuliana Prodan <iuliana.prodan@....com>
To:     Ard Biesheuvel <ardb@...nel.org>,
        "Iuliana Prodan (OSS)" <iuliana.prodan@....nxp.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Horia Geanta <horia.geanta@....com>,
        Aymen Sghaier <aymen.sghaier@....com>,
        Silvano Di Ninno <silvano.dininno@....com>,
        Franck Lenormand <franck.lenormand@....com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-imx <linux-imx@....com>
Subject: Re: [RFC PATCH 0/4] crypto: add CRYPTO_TFM_REQ_DMA flag

On 11/25/2020 11:16 PM, Ard Biesheuvel wrote:
> On Wed, 25 Nov 2020 at 22:14, Iuliana Prodan (OSS)
> <iuliana.prodan@....nxp.com> wrote:
>>
>> From: Iuliana Prodan <iuliana.prodan@....com>
>>
>> Add the option to allocate the crypto request object plus any extra space
>> needed by the driver into a DMA-able memory.
>>
>> Add CRYPTO_TFM_REQ_DMA flag to be used by backend implementations to
>> indicate to crypto API the need to allocate GFP_DMA memory
>> for private contexts of the crypto requests.
>>
> 
> These are always directional DMA mappings, right? So why can't we use
> bounce buffering here?
> 
The idea was to avoid allocating any memory in crypto drivers.
We want to be able to use dm-crypt with CAAM, which needs DMA-able 
memory and increasing reqsize is not enough.
It started from here 
https://lore.kernel.org/linux-crypto/71b6f739-d4a8-8b26-bf78-ce9acf9a0f99@nxp.com/T/#m39684173a2f0f4b83d8bcbec223e98169273d1e4

>> For IPsec use cases, CRYPTO_TFM_REQ_DMA flag is also checked in
>> esp_alloc_tmp() function for IPv4 and IPv6.
>>
>> This series includes an example of how a driver can use
>> CRYPTO_TFM_REQ_DMA flag while setting reqsize to a larger value
>> to avoid allocating memory at crypto request runtime.
>> The extra size needed by the driver is added to the reqsize field
>> that indicates how much memory could be needed per request.
>>
>> Iuliana Prodan (4):
>>    crypto: add CRYPTO_TFM_REQ_DMA flag
>>    net: esp: check CRYPTO_TFM_REQ_DMA flag when allocating crypto request
>>    crypto: caam - avoid allocating memory at crypto request runtime for
>>      skcipher
>>    crypto: caam - avoid allocating memory at crypto request runtime for
>>      aead
>>
>>   drivers/crypto/caam/caamalg.c | 130 +++++++++++++++++++++++++---------
>>   include/crypto/aead.h         |   4 ++
>>   include/crypto/akcipher.h     |  21 ++++++
>>   include/crypto/hash.h         |   4 ++
>>   include/crypto/skcipher.h     |   4 ++
>>   include/linux/crypto.h        |   1 +
>>   net/ipv4/esp4.c               |   7 +-
>>   net/ipv6/esp6.c               |   7 +-
>>   8 files changed, 144 insertions(+), 34 deletions(-)
>>
>> --
>> 2.17.1
>>