linux-kernel - Re: [PATCH 1/3] crypto: X25519 low-level primitives for ppc64le.

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Date: Wed, 15 May 2024 11:06:58 +0200
From: Andy Polyakov <appro@...ptogams.org>
To: Danny Tsen <dtsen@...ux.ibm.com>, linux-crypto@...r.kernel.org
Cc: herbert@...dor.apana.org.au, leitao@...ian.org, nayna@...ux.ibm.com,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 mpe@...erman.id.au, ltcgcw@...ux.vnet.ibm.com, dtsen@...ibm.com
Subject: Re: [PATCH 1/3] crypto: X25519 low-level primitives for ppc64le.

Hi,

> +SYM_FUNC_START(x25519_fe51_sqr_times)
> ...
> +
> +.Lsqr_times_loop:
> ...
> +
> +	std	9,16(3)
> +	std	10,24(3)
> +	std	11,32(3)
> +	std	7,0(3)
> +	std	8,8(3)
> +	bdnz	.Lsqr_times_loop

I see no reason for why the stores can't be moved outside the loop in 
question.

> +SYM_FUNC_START(x25519_fe51_frombytes)
> +.align	5
> +
> +	li	12, -1
> +	srdi	12, 12, 13	# 0x7ffffffffffff
> +
> +	ld	5, 0(4)
> +	ld	6, 8(4)
> +	ld	7, 16(4)
> +	ld	8, 24(4)

Is there actual guarantee that the byte input is 64-bit aligned? While 
it is true that processor is obliged to handle misaligned loads and 
stores by the ISA specification, them being inefficient doesn't go 
against it. Most notably inefficiency is likely to be noted at the page 
boundaries. What I'm trying to say is that it would be more appropriate 
to avoid the unaligned loads (and stores).

Cheers.