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Date:   Thu, 26 Nov 2020 18:12:55 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Iuliana Prodan <iuliana.prodan@....com>
Cc:     Horia Geanta <horia.geanta@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        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>,
        "Iuliana Prodan (OSS)" <iuliana.prodan@....nxp.com>
Subject: Re: [RFC PATCH 0/4] crypto: add CRYPTO_TFM_REQ_DMA flag

On Thu, 26 Nov 2020 at 17:00, Iuliana Prodan <iuliana.prodan@....com> wrote:
>
> On 11/26/2020 9:09 AM, Ard Biesheuvel wrote:
> > On Wed, 25 Nov 2020 at 22:39, Iuliana Prodan <iuliana.prodan@....com> wrote:
> >>
> >> 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.
> >
> > But what does 'needs DMA-able memory' mean? DMA operations are
> > asynchronous by definition, and so the DMA layer should be able to
> > allocate bounce buffers when needed. This will cost some performance
> > in cases where the hardware cannot address all of memory directly, but
> > this is a consequence of the design, and I don't think we should
> > burden the generic API with this.
> >
> Ard, I believe you're right.
>
> In CAAM, for req->src and req->dst, which comes from crypto request, we
> use DMA mappings without knowing if the memory is DMAable or not.
>
> We should do the same for CAAM's hw descriptors commands and link
> tables. That's the extra memory allocated by increasing reqsize.
>

It depends on whether any such mappings are non-directional. But I
would not expect per-request mappings to be modifiable by both the CPU
and the device at the same time.


> Horia, do you see any limitations, in CAAM, for not using the above
> approach?
>
>
> >> It started from here
> >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flinux-crypto%2F71b6f739-d4a8-8b26-bf78-ce9acf9a0f99%40nxp.com%2FT%2F%23m39684173a2f0f4b83d8bcbec223e98169273d1e4&amp;data=04%7C01%7Ciuliana.prodan%40nxp.com%7C436d50e009434fd1c52808d891da3c8f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637419713794116972%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=38rJuxFhPWDJXWc2R66Hu%2Fn7vve9u%2BeF0Evp%2BFAhCwQ%3D&amp;reserved=0
> >>
> >>>> 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
> >>>>

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