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

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Message-ID: <aB4ONRiTNjHpCw6U@gondor.apana.org.au>
Date: Fri, 9 May 2025 22:16:21 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
Cc: 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>,
	Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] crypto: powerpc/poly1305 - Restore crypto_simd_usable
 test

On Thu, May 08, 2025 at 08:23:17PM +0800, Herbert Xu wrote:
>
> @@ -51,7 +52,7 @@ void poly1305_blocks_arch(struct poly1305_block_state *state, const u8 *src,
>  	if (!static_key_enabled(&have_p10))
>  		return poly1305_blocks_generic(state, src, len, padbit);
>  	vsx_begin();
> -	if (len >= POLY1305_BLOCK_SIZE * 4) {
> +	if (crypto_simd_usable() && len >= POLY1305_BLOCK_SIZE * 4) {

This patch is obviously broken.  However, I think this code was
always broken in the SIMD-fallback case.  AFAICS the fallback
uses vector instructions so it can't be used in softirqs either.

A proper fallback would have to convert the state to the format
used by the generic poly1305 implementation, call that, and then
convert it back.

Of course it would be a lot easier if ppc could make VSX usable
in softirq context.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt