linux-kernel - Re: [PATCH v2 5.4 regression fix] x86/boot: Provide memzero

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Message-ID: <20191007184237.GB13589@rani.riverdale.lan>
Date:   Mon, 7 Oct 2019 14:42:37 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Hans de Goede <hdegoede@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Stephan Mueller <smueller@...onox.de>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH v2 5.4 regression fix] x86/boot: Provide memzero_explicit

On Mon, Oct 07, 2019 at 05:40:07PM +0200, Ingo Molnar wrote:
> 
> * Arvind Sankar <nivedita@...m.mit.edu> wrote:
> 
> > With the barrier in there, is there any reason to *not* inline the
> > function? barrier_data() is an asm statement that tells the compiler
> > that the asm uses the memory that was set to zero, thus preventing it
> > from removing the memset even if nothing else uses that memory later. A
> > more detailed comment is there in compiler-gcc.h. I can't see why it
> > wouldn't work even if it were inlined.
> > 
> > If the function can indeed be inlined, we could just make the common
> > implementation a macro and avoid duplicating it? As mentioned in another
> > mail, we otherwise will likely need another duplicate implementation for
> > arch/s390/purgatory as well.
> 
> I suspect macro would be justified in this case. Mind sending a v3 patch 
> to demonstrate how it would all look like?
> 
> I'll zap v2 if the macro solution looks better.
> 
> Thanks,
> 
> 	Ingo

Patch attached to turn memzero_explicit into inline function.

View attachment "0001-lib-string-make-memzero_explicit-inline-instead-of-e.patch" of type "text/x-diff" (2882 bytes)