Re: [v2 PATCH] crypto: powerpc/poly1305 - Add poly1305_emit_arch wrapper

[Eric Biggers <ebiggers@kernel.org>]

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