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Date: Tue, 15 Jul 2014 18:32:23 +0400
From: Andrey Ryabinin <a.ryabinin@samsung.com>
Subject: Re: [RFC/PATCH -next 00/21] Address sanitizer for kernel (kasan) -
 dynamic memory error detector.
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To: Christoph Lameter <cl@gentwo.org>, Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>, Konstantin Serebryany <kcc@google.com>, Alexey Preobrazhensky <preobr@google.com>, Andrey Konovalov <adech.fo@gmail.com>, Yuri Gribov <tetra2005@gmail.com>, Konstantin Khlebnikov <koct9i@gmail.com>, Sasha Levin <sasha.levin@oracle.com>, Michal Marek <mmarek@suse.cz>, Russell King <linux@arm.linux.org.uk>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, linux-kbuild@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-mm@kvack.org

On 07/14/14 19:13, Christoph Lameter wrote:
> On Sun, 13 Jul 2014, Andrey Ryabinin wrote:
> 
>>> How does that work when memory is sparsely populated?
>>>
>>
>> Sparsemem configurations currently may not work with kasan.
>> I suppose I will have to move shadow area to vmalloc address space and
>> make it (shadow) sparse too if needed.
> 
> Well it seems to work with sparsemem / vmemmap? So non vmmemmapped configs
> of sparsemem only. vmemmmap can also handle holes in memory.
> 
> 

Not sure. This sparsemem/vmemmap thing is kinda new to me, so I need to dig some more
to understand how it iтteracts with kasan.

As far as I understand the main problem with sparsemem & kasan is shadow allocation:

	unsigned long lowmem_size = (unsigned long)high_memory - PAGE_OFFSET;
	shadow_size = lowmem_size >> KASAN_SHADOW_SCALE_SHIFT;

	shadow_phys_start = memblock_alloc(shadow_size, PAGE_SIZE);

If we don't have one big enough physically contiguous block for shadow it will fail.