linux-kernel - Re: [PATCH v4 08/13] crypto: s390/sha256 - implement library instead of shash

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Message-ID: <20250601230014.GB1228@sol>
Date: Sun, 1 Jun 2025 16:00:14 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Alex Williamson <alex.williamson@...hat.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-riscv@...ts.infradead.org, sparclinux@...r.kernel.org,
	linux-s390@...r.kernel.org, x86@...nel.org,
	Ard Biesheuvel <ardb@...nel.org>,
	"Jason A . Donenfeld" <Jason@...c4.com>
Subject: Re: [PATCH v4 08/13] crypto: s390/sha256 - implement library instead
 of shash

On Fri, May 30, 2025 at 12:18:58AM +0000, Eric Biggers wrote:
> On Thu, May 29, 2025 at 04:54:34PM -0700, Linus Torvalds wrote:
> > On Thu, 29 May 2025 at 14:16, Eric Biggers <ebiggers@...nel.org> wrote:
> > >
> > > So using crc32c() + ext4 + x86 as an example (but SHA-256 would be very
> > > similar), the current behavior is that ext4.ko depends on the crc32c_arch()
> > > symbol.
> > 
> > Yes, I think that's a good example.
> > 
> > I think it's an example of something that "works", but it certainly is
> > a bit hacky.
> > 
> > Wouldn't it be nicer if just plain "crc32c()" did the right thing,
> > instead of users having to do strange hacks just to get the optimized
> > version that they are looking for?
> 
> For crc32c() that's exactly how it works (since v6.14, when I implemented it).
> The users call crc32c() which is an inline function, which then calls
> crc32c_arch() or crc32c_base() depending on the kconfig.  So that's why I said
> the symbol dependency is currently on crc32c_arch.  Sorry if I wasn't clear.
> The SHA-256, ChaCha, and Poly1305 library code now has a similar design too.
> 
> If we merged the arch and generic modules together, then the symbol would become
> crc32c.  But in either case crc32c() is the API that all the users call.
> 
> - Eric
> 

I implemented my proposal, for lib/crc first, in
https://lore.kernel.org/lkml/20250601224441.778374-1-ebiggers@kernel.org.
I think it's strictly better than the status quo, and once applied to lib/crypto
it will solve some of the problems we've been having there too.  But let me know
if you still have misgivings.

- Eric