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

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Date:   Fri, 15 Sep 2017 07:34:31 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Mathias Krause <minipli@...glemail.com>,
        Chandramouli Narayanan <mouli@...ux.intel.com>,
        Jussi Kivilinna <jussi.kivilinna@....fi>,
        Peter Zijlstra <peterz@...radead.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>,
        Andy Lutomirski <luto@...nel.org>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH 00/12] x86/crypto: Fix RBP usage in several crypto .S
 files


* Eric Biggers <ebiggers3@...il.com> wrote:

> 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@...hat.com>
> > 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!

Cool, thanks for review and the testing! Can we add your Tested-by + Acked-by tags 
to the patches?

Thanks,

	Ingo