linux-kernel - Re: [PATCH 1/3] memblock, nobootmem: Add memblock_virt_alloc

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Date:	Tue, 28 Jan 2014 13:56:52 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Yinghai Lu <yinghai@...nel.org>,
	Kevin Hilman <khilman@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Dave Hansen <dave.hansen@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Strashko, Grygorii" <grygorii.strashko@...com>,
	xen-devel@...ts.xensource.com
Subject: Re: [PATCH 1/3] memblock, nobootmem: Add memblock_virt_alloc_low()

On Tue, Jan 28, 2014 at 01:36:28PM -0500, Santosh Shilimkar wrote:
> + Gryagorii,
> On Tuesday 28 January 2014 01:22 PM, Russell King - ARM Linux wrote:
> > On Tue, Jan 28, 2014 at 12:23:02PM -0500, Santosh Shilimkar wrote:
> >> On Tuesday 28 January 2014 12:12 PM, Yinghai Lu wrote:
> >>> Index: linux-2.6/include/linux/bootmem.h
> >>> ===================================================================
> >>> --- linux-2.6.orig/include/linux/bootmem.h
> >>> +++ linux-2.6/include/linux/bootmem.h
> >>> @@ -179,6 +179,9 @@ static inline void * __init memblock_vir
> >>>                                                     NUMA_NO_NODE);
> >>>  }
> >>>
> >>> +/* Take arch's ARCH_LOW_ADDRESS_LIMIT at first*/
> >>> +#include <asm/processor.h>
> >>> +
> >>>  #ifndef ARCH_LOW_ADDRESS_LIMIT
> >>>  #define ARCH_LOW_ADDRESS_LIMIT  0xffffffffUL
> >>>  #endif
> >>
> >> This won't help mostly since the ARM 32 arch don't set ARCH_LOW_ADDRESS_LIMIT.
> >> Sorry i couldn't respond to the thread earlier because of travel and
> >> don't have access to my board to try out the patches.
> > 
> > Let's think about this for a moment, shall we...
> > 
> > What does memblock_alloc_virt*() return?  It returns a virtual address.
> > 
> > How is that virtual address obtained?  ptr = phys_to_virt(alloc);
> > 
> > What is the valid address range for passing into phys_to_virt() ?  Only
> > lowmem addresses.
> > 
> > Hence, having ARCH_LOW_ADDRESS_LIMIT set to 4GB-1 by default seems to be
> > completely rediculous - and presumably this also fails on x86_32 if it
> > returns memory up at 4GB.
> > 
> > So... yes, I think reverting the arch/arm part of this patch is the right
> > solution, whether the rest of it should be reverted is something I can't
> > comment on.
> > 
> Grygorri mentioned an alternate to update the memblock_find_in_range_node() so
> that it takes into account the limit.

This patch breaks also Xen and 32-bit guests (see
http://lists.xen.org/archives/html/xen-devel/2014-01/msg02476.html)

Reverting it fixes it.

> 
> Regards,
> Santosh 
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