Subject: Re: [PATCH 15/36] lib/crypto: s390/aes: Migrate optimized code into library

From: Holger Dengler <[email-masked]>
Date: Wed, 7 Jan 2026 08:41:02 +0100

Hi Eric,

first of all: happy New Year! ANd thanks for the series.

On 05/01/2026 06:12, Eric Biggers wrote:
> Implement aes_preparekey_arch(), aes_encrypt_arch(), and 
> aes_decrypt_arch() using the CPACF AES instructions.

I'm not sure, it it makes sense to implement this on s390 at all. The CPACF
instructions cover full modes of operations and are optimized to process more
than one cipher-block-size (*). For single-block operations, the performance
might be worth than using the generic functions. I will look into it and do
some performance tests. If there is a possibility to plug-in to the level
where the modes of operation are implemented, it would make much more sense
for s390.

(*) Yes, it's a bit uncommon, but the CPACF instructions on s390 can process
multiple block with a single instruction call! They are so called long running
instructions.

> Then, remove the superseded "aes-s390" crypto_cipher.
> 
> The result is that both the AES library and crypto_cipher APIs use the 
> CPACF AES instructions, whereas previously only crypto_cipher did (and it 
> wasn't enabled by default, which this commit fixes as well).
> 
> Note that this preserves the optimization where the AES key is stored in 
> raw form rather than expanded form.  CPACF just takes the raw key.
> 
> Signed-off-by: Eric Biggers <[email-masked]> --- arch/s390/crypto/

-- Mit freundlichen Grüßen / Kind regards
Holger Dengler
--
IBM Systems, Linux on IBM Z Development
[email-masked]