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Subject: Re: [PATCH v2 5.4 regression fix] x86/boot: Provide memzero_explicit
To:     Arvind Sankar <nivedita@alum.mit.edu>,
        Ingo Molnar <mingo@kernel.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        linux-crypto@vger.kernel.org, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Stephan Mueller <smueller@chronox.de>,
        linux-s390@vger.kernel.org
References: <20191007134724.4019-1-hdegoede@redhat.com>
 <20191007140022.GA29008@gmail.com>
 <1dc3c53d-785e-f9a4-1b4c-3374c94ae0a7@redhat.com>
 <20191007142230.GA117630@gmail.com>
 <2982b666-e310-afb7-40eb-e536ce95e23d@redhat.com>
 <20191007144600.GB59713@gmail.com>
 <20191007152049.GA384920@rani.riverdale.lan>
 <20191007154007.GA96929@gmail.com>
 <20191007184237.GB13589@rani.riverdale.lan>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <1d17349e-98ab-b582-6981-b484b0e970b6@redhat.com>
Date:   Mon, 7 Oct 2019 21:36:25 +0200
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Hi,

On 07-10-2019 20:42, Arvind Sankar wrote:
> On Mon, Oct 07, 2019 at 05:40:07PM +0200, Ingo Molnar wrote:
>>
>> * Arvind Sankar <nivedita@alum.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.

Hehe, I had prepared and have just tested the exact same patch
(only the commit msg was different).

I've just booted a kernel build with that patch and that works
fine (as expected).

So your patch is:

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>

Since this is a bit of a core change though, I think it is
best if you send it to the linux-kernel list (with my tags from above
added) as is normally done for kernel patches. Then others, who may
not be following this thread, will get a chance to give feedback on it.

Regards,

Hans