linux-kernel - Re: [PATCH v10 02/17] x86

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Message-Id: <20150130133723.26e6e7f2b8e489a8640abd05@linux-foundation.org>
Date:	Fri, 30 Jan 2015 13:37:23 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
Cc:	linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
	Andy Lutomirski <luto@...capital.net>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v10 02/17] x86_64: add KASan support

On Fri, 30 Jan 2015 19:15:42 +0300 Andrey Ryabinin <a.ryabinin@...sung.com> wrote:

> >> --- a/lib/Kconfig.kasan
> >> +++ b/lib/Kconfig.kasan
> >> @@ -5,6 +5,7 @@ if HAVE_ARCH_KASAN
> >>  
> >>  config KASAN
> >>  	bool "AddressSanitizer: runtime memory debugger"
> >> +	depends on !MEMORY_HOTPLUG
> >>  	help
> >>  	  Enables address sanitizer - runtime memory debugger,
> >>  	  designed to find out-of-bounds accesses and use-after-free bugs.
> > 
> > That's a significant restriction.  It has obvious runtime implications.
> > It also means that `make allmodconfig' and `make allyesconfig' don't
> > enable kasan, so compile coverage will be impacted.
> > 
> > This wasn't changelogged.  What's the reasoning and what has to be done
> > to fix it?
> > 
> 
> Yes, this is runtime dependency. Hot adding memory won't work.
> Since we don't have shadow for hotplugged memory, kernel will crash on the first access to it.
> To fix this we need to allocate shadow for new memory.
> 
> Perhaps it would be better to have a runtime warning instead of Kconfig dependecy?

Is there a plan to get mem-hotplug working with kasan, btw?  It doesn't
strike me as very important/urgent.  Please add a sentence about this
to the changelog as well.
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