From: Ard Biesheuvel <ardb@kernel.org>
To: Linux Crypto Mailing List <linux-crypto@vger.kernel.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
Eric Biggers <ebiggers@google.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 0/7] crypto: switch to static calls for CRC-T10DIF
Date: Mon, 11 Jan 2021 19:36:20 +0100 [thread overview]
Message-ID: <CAMj1kXHLBDUGZbc7dw0bd5K4ecPLmnDYMwrPA7yGzA0VNaJWgw@mail.gmail.com> (raw)
In-Reply-To: <CAMj1kXEBPjmCGPPme=rXqadLQeNdqzeyr7uw1WsUoHUqQv1_LQ@mail.gmail.com>
On Mon, 11 Jan 2021 at 18:27, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Mon, 11 Jan 2021 at 17:52, Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > CRC-T10DIF is a very poor match for the crypto API:
> > - every user in the kernel calls it via a library wrapper around the
> > shash API, so all callers share a single instance of the transform
> > - each architecture provides at most a single optimized implementation,
> > based on SIMD instructions for carryless multiplication
> >
> > In other words, none of the flexibility it provides is put to good use,
> > and so it is better to get rid of this complexity, and expose the optimized
> > implementations via static calls instead. This removes a substantial chunk
> > of code, and also gets rid of any indirect calls on architectures that
> > obsess about those (x86)
> >
> > If this approach is deemed suitable, there are other places where we might
> > consider adopting it: CRC32 and CRC32(C).
> >
> > Patch #1 does some preparatory refactoring and removes the library wrapper
> > around the shash transform.
> >
> > Patch #2 introduces the actual static calls, along with the registration
> > routines to update the crc-t10dif implementation at runtime.
> >
> > Patch #3 updates the generic CRC-T10DIF shash driver so it distinguishes
> > between the optimized library code and the generic library code.
> >
> > Patches #4 to #7 update the various arch implementations to switch over to
> > the new method.
> >
> > Special request to Peter to take a look at patch #2, and in particular,
> > whether synchronize_rcu_tasks() is sufficient to ensure that a module
> > providing the target of a static call can be unloaded safely.
> >
>
> It seems I may have managed to confuse myself slightly here: without
> an upper bound on the size of the input of the crc_t10dif() routine, I
> suppose we can never assume that all its callers have finished.
>
Replying to self again - apologies.
I think this is actually correct after all: synchronize_rcu_tasks()
guarantees that all tasks have passed through a 'safe state', i.e.,
voluntary schedule(), return to userland, etc, which guarantees that
no task could be executing the old static call target after
synchronize_rcu_tasks() returns.
next prev parent reply other threads:[~2021-01-11 18:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-11 16:52 [PATCH 0/7] crypto: switch to static calls for CRC-T10DIF Ard Biesheuvel
2021-01-11 16:52 ` [PATCH 1/7] crypto: crc-t10dif - turn library wrapper for shash into generic library Ard Biesheuvel
2021-01-11 16:52 ` [PATCH 2/7] crypto: lib/crc-t10dif - add static call support for optimized versions Ard Biesheuvel
2021-01-11 16:52 ` [PATCH 3/7] crypto: generic/crc-t10dif - expose both arch and generic shashes Ard Biesheuvel
2021-01-11 16:52 ` [PATCH 4/7] crypto: x86/crc-t10dif - convert to static call library API Ard Biesheuvel
2021-01-12 0:01 ` kernel test robot
2021-01-12 0:01 ` kernel test robot
2021-01-11 16:52 ` [PATCH 5/7] crypto: arm/crc-t10dif " Ard Biesheuvel
2021-01-11 16:52 ` [PATCH 6/7] crypto: arm64/crc-t10dif - convert to static call API Ard Biesheuvel
2021-01-11 16:52 ` [PATCH 7/7] crypto: powerpc/crc-t10dif " Ard Biesheuvel
2021-01-11 17:27 ` [PATCH 0/7] crypto: switch to static calls for CRC-T10DIF Ard Biesheuvel
2021-01-11 18:36 ` Ard Biesheuvel [this message]
2021-01-11 20:56 ` Peter Zijlstra
2021-01-11 21:01 ` Ard Biesheuvel
2021-01-11 21:05 ` Eric Biggers
2021-01-11 21:31 ` Ard Biesheuvel
2021-01-28 8:19 ` Ard Biesheuvel
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