Re: [PATCH 00/12] x86/crypto: Fix RBP usage in several crypto .S files

From: Eric Biggers
Date: Fri Sep 15 2017 - 00:55:05 EST

Hi Josh,

On Wed, Sep 13, 2017 at 05:33:03PM -0500, Josh Poimboeuf wrote:
> And here's v2 of the sha512-avx2 patch. It should hopefully gain back
> most of the performance lost by v1.
> From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Subject: [PATCH] x86/crypto: Fix RBP usage in sha512-avx2-asm.S
> Using RBP as a temporary register breaks frame pointer convention and
> breaks stack traces when unwinding from an interrupt in the crypto code.
> Mix things up a little bit to get rid of the RBP usage, without
> destroying performance. Use RDI instead of RBP for the TBL pointer.
> That will clobber CTX, so save CTX on the stack and use RDI as CTX
> before it gets clobbered, and R12 as CTX after it gets clobbered.
> Also remove the unused y4 variable.

I tested the v2 patches for both sha256-avx2 and sha512-avx2 on Skylake. They
both pass the crypto self-tests, and there was no noticable performance
difference compared to the unpatched versions. Thanks!