linux-kernel - Re: [PATCH v2 04/20] crypto: aegis128-neon - Move to more abstract 'ksimd' guard API

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Message-ID: <CAMj1kXEK+ggQXC6pruZs2jkg6fmA7+Uv45DY4B_XqTRsRbTf2Q@mail.gmail.com>
Date: Thu, 2 Oct 2025 18:48:35 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Kees Cook <kees@...nel.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-arm-kernel@...ts.infradead.org, 
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	herbert@...dor.apana.org.au, linux@...linux.org.uk, 
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Catalin Marinas <catalin.marinas@....com>, Mark Brown <broonie@...nel.org>, 
	Eric Biggers <ebiggers@...nel.org>
Subject: Re: [PATCH v2 04/20] crypto: aegis128-neon - Move to more abstract
 'ksimd' guard API

On Thu, 2 Oct 2025 at 18:20, Kees Cook <kees@...nel.org> wrote:
>
> On Wed, Oct 01, 2025 at 11:02:06PM +0200, Ard Biesheuvel wrote:
> > From: Ard Biesheuvel <ardb@...nel.org>
> >
> > Move away from calling kernel_neon_begin() and kernel_neon_end()
> > directly, and instead, use the newly introduced scoped_ksimd() API. This
> > permits arm64 to modify the kernel mode NEON API without affecting code
> > that is shared between ARM and arm64.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > ---
> >  crypto/aegis128-neon.c | 33 +++++++-------------
> >  1 file changed, 12 insertions(+), 21 deletions(-)
> >
> > diff --git a/crypto/aegis128-neon.c b/crypto/aegis128-neon.c
> > index 9ee50549e823..b41807e63bd3 100644
> > --- a/crypto/aegis128-neon.c
> > +++ b/crypto/aegis128-neon.c
> > @@ -4,7 +4,7 @@
> >   */
> >
> >  #include <asm/cpufeature.h>
> > -#include <asm/neon.h>
> > +#include <asm/simd.h>
> >
> >  #include "aegis.h"
> >  #include "aegis-neon.h"
> > @@ -24,32 +24,28 @@ void crypto_aegis128_init_simd(struct aegis_state *state,
> >                              const union aegis_block *key,
> >                              const u8 *iv)
> >  {
> > -     kernel_neon_begin();
> > -     crypto_aegis128_init_neon(state, key, iv);
> > -     kernel_neon_end();
> > +     scoped_ksimd()
> > +             crypto_aegis128_init_neon(state, key, iv);
> >  }
>
> For these cases (to avoid the indentation change), do you want to use
> just "guard" instead of "scope_guard", or do you want to explicitly
> require explicit scope context even when the scope ends at the function
> return?
>

I'm on the fence tbh. I think for future maintainability, being forced
to define the scope is perhaps better but in this case, the whole
function contains only a single line so there is little room for
confusion.