linux-kernel - Re: [v3 PATCH] crypto: lib/Kconfig

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Message-Id: <ca6ebfce-1969-4e13-94de-96702540a967@app.fastmail.com>
Date: Fri, 28 Feb 2025 18:10:28 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Herbert Xu" <herbert@...dor.apana.org.au>
Cc: "Arnd Bergmann" <arnd@...nel.org>, "Will Deacon" <will@...nel.org>,
 "David S . Miller" <davem@...emloft.net>,
 "Catalin Marinas" <catalin.marinas@....com>,
 "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "Harald Freudenberger" <freude@...ux.ibm.com>,
 "Holger Dengler" <dengler@...ux.ibm.com>,
 "Heiko Carstens" <hca@...ux.ibm.com>, "Vasily Gorbik" <gor@...ux.ibm.com>,
 "Alexander Gordeev" <agordeev@...ux.ibm.com>,
 "Christian Borntraeger" <borntraeger@...ux.ibm.com>,
 "Sven Schnelle" <svens@...ux.ibm.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>,
 "Ard Biesheuvel" <ardb@...nel.org>, "Eric Biggers" <ebiggers@...gle.com>,
 "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
 "Jarkko Sakkinen" <jarkko@...nel.org>, linux-crypto@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mips@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [v3 PATCH] crypto: lib/Kconfig - Hide arch options from user

On Fri, Feb 28, 2025, at 05:11, Herbert Xu wrote:
> On Thu, Feb 27, 2025 at 12:56:30PM +0100, Arnd Bergmann wrote:
>>
>> I've tried to undo that portion here and don't run into a
>> dependency loop so far with the patch below on top of yours
>> (around 100 randconfigs in). I'll keep testing and will let
>> you know when something goes wrong.
>
> That's because you removed 'select CRYPTO', which can cause the
> arch code to silently disappear just like my original patch.
>
> It's pretty much difficult to disable CRYPTO because so many
> random things select it.  But I managed to turn CRYPTO off with
> some effort and indeed with your patch the arch code disappears.
>
> In the following config file, CONFIG_CRYPTO_LIB_CHACHA is modular but
> the X86 option for it is not selected, because CRYPTO itself is off.

I see. So the case of building lib/crypto code but not CONFIG_CRYPTO
is something I would normally expect to work, including the
architecture specific optimizations, and it's probably not
too hard to get there, but it's also unclear if there is really a
point in doing that.

For design purity, I think we would need to split the architecture
specific code the same way as the generic ones: library functions
that always get selected by their users to export functions and
the front-ends that are user-selectable and register the algorithm
with the crypto API.

Keeping the 'select CRYPTO' is clearly less effor if you prefer
that.

      Arnd