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

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Message-ID: <20191007154007.GA96929@gmail.com>
Date:   Mon, 7 Oct 2019 17:40:07 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     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>
Subject: Re: [PATCH v2 5.4 regression fix] x86/boot: Provide memzero_explicit


* 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