linux-ext4 - Re: [RFC 1/1] mm: add virt to phys debug

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Date:	Thu, 1 May 2008 13:18:42 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Jiri Slaby <jirislaby@...il.com>
cc:	linux-mm@...ck.org, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>, pageexec@...email.hu,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	herbert@...dor.apana.org.au, penberg@...helsinki.fi,
	akpm@...ux-foundation.org, linux-ext4@...r.kernel.org,
	paulmck@...ux.vnet.ibm.com, rjw@...k.pl, zdenek.kabelac@...il.com,
	David Miller <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC 1/1] mm: add virt to phys debug

On Thu, 1 May 2008, Jiri Slaby wrote:

> Christoph, was you able to compile this somehow? I had to move the code
> into ioremap along 64-bit variant to allow the checking.

The 64 bit piece works fine here and I used it for debugging the vmalloc 
work. Not sure about the 32 bit piece.

> A pacth which I created is attached, I've successfully tested it by this
> module:

Great! Someone else picks this up. You can probably do a more thorough 
job than I can.

> Add some (configurable) expensive sanity checking to catch wrong address
> translations on x86.
> 
> - create linux/mmdebug.h file to be able include this file in
>   asm headers to not get unsolvable loops in header files
> - __phys_addr on x86_32 became a function in ioremap.c since
>   PAGE_OFFSET and is_vmalloc_addr is undefined if declared in
>   page_32.h (again circular dependencies)
> - add __phys_addr_const for initializing doublefault_tss.__cr3

Hmmm.. We could use include/linux/bounds.h to make 
VMALLOC_START/VMALLOC_END (or whatever you need for checking the memory 
boundaries) a cpp constant which may allow the use in page_32.h without 
circular dependencies.


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