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Date: Mon, 23 Oct 2017 10:08:30 +0100
From: Mark Rutland <>
To: Peter Zijlstra <>
Cc: Alexander Popov <>,,,,,
	Ingo Molnar <>, Andy Lutomirski <>,, Laura Abbott <>,
	Ard Biesheuvel <>,
	Borislav Petkov <>,
	Thomas Gleixner <>,
	"H . Peter Anvin" <>,
Subject: Re: [PATCH RFC v5 0/5] Introduce the STACKLEAK feature and a test
 for it

On Sun, Oct 22, 2017 at 03:11:57PM +0200, Peter Zijlstra wrote:
> On Sun, Oct 22, 2017 at 03:22:48AM +0300, Alexander Popov wrote:
> > Further work
> > =============
> > 
> >  - Rewrite erase_kstack() in C (if Ingo Molnar insists).
> Aside from legacy, is there any sane reason that stuff is in ASM? That
> is, I too will insist it being in C unless you can provide good
> arguments on why it needs be asm. All it does is memzero() right? And I
> would think architectures already have fairly optimized implementations
> of that around.

One argument for this being in asm is that you can't control the stack
usage of a C implementation of erase_kstack(), which leaves a (small)
portion of the stack potentially not cleared depending on what exactly
the compiler does with the stack.

If it's just a call to memzero(), the asm should be very simple, and I'd
think it's better to err on the side of clearing as much of the stack as


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