linux-kernel - Re: [v2 PATCH] crypto: powerpc/poly1305

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Message-ID: <20250510053308.GB505731@sol>
Date: Fri, 9 May 2025 22:33:08 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>,
	Thorsten Leemhuis <linux@...mhuis.info>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Next Mailing List <linux-next@...r.kernel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Danny Tsen <dtsen@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [v2 PATCH] crypto: powerpc/poly1305 - Add poly1305_emit_arch
 wrapper

On Sat, May 10, 2025 at 01:10:22PM +0800, Herbert Xu wrote:
> On Fri, May 09, 2025 at 09:44:50PM -0700, Eric Biggers wrote:
> >
> > This fixes "-cpu Power10", but older CPUs (e.g. "-cpu POWER9") are still
> > failing.
> 
> You're right.  I'll revert this and apply the following patch
> instead.
> 
> BTW this thing is still hopelessly broken if it's called from
> softirq context because there is no SIMD fallback.  Yes I removed
> the SIMD check but it was already broken before that as it simply
> switched from the 4-block version to the 1-block version if SIMD
> is not available rather than actually doing something that is
> safe in softirq context.
> 
> Perhaps we should just remove this altogether until it's fixed.

Yes, the PowerPC Poly1305 code incorrectly uses VSX without first checking
crypto_simd_usable().  And PowerPC also doesn't support VSX in softirqs, or at
least it doesn't claim to (it doesn't override may_use_simd(), so it gets the
default from include/asm-generic/simd.h which returns false in softirq context).
Maybe add 'depends on BROKEN' to CRYPTO_POLY1305_P10 for now, and give the
PowerPC folks (Cc'ed) a chance to fix this before removing the code.

- Eric