linux-kernel - Re: x86-64: memset()/memcpy() not fully standards compliant

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Message-Id: <4F06F640020000780006ACDE@nat28.tlf.novell.com>
Date:	Fri, 06 Jan 2012 12:25:20 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: x86-64: memset()/memcpy() not fully standards compliant

>>> On 06.01.12 at 12:08, Andi Kleen <andi@...stfloor.org> wrote:
>>  It's not the traditional bootmem implementation anymore, but
>> alloc_bootmem() et al still exist, and still clear the allocated memory
>> (in __alloc_memory_core_early()). So there is a code path that can
>> validly be used (and it is this code path that is presenting one of the
>> problems with the non-pv-ops Xen kernels, as they're using flatmem
>> rather than sparsemem since their physical address space is always
>> fully continuous).
> 
> Yes but there should be no callers that do alloc_bootmem(4G)
> The biggest ones afak are the 1GB pages I added some time ago.
> 
> How is it a problem in the non pv Xen kernels?

pgdat->node_mem_map[] exceeds 4G when total memory goes far
enough beyond 292G. At some later point ->node_page_cgroup[]
also exceeds 4G. Finally, the phys-to-machine mapping (which gets
resized during boot) exceeds 4G when crossing the 2T boundary.

Jan

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