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

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Message-ID: <20140128182230.GO15937@n2100.arm.linux.org.uk>
Date:	Tue, 28 Jan 2014 18:22:30 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	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>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH 1/3] memblock, nobootmem: Add memblock_virt_alloc_low()

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.

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