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Date: Mon, 13 Nov 2017 10:57:16 +0530
From: Kaiwan N Billimoria <>
To: "Tobin C. Harding" <>
Cc: "Kirill A. Shutemov" <>,, 
	"Jason A. Donenfeld" <>, "Theodore Ts'o" <>, 
	Linus Torvalds <>, Kees Cook <>, 
	Paolo Bonzini <>, Tycho Andersen <>, 
	"Roberts, William C" <>, Tejun Heo <>, 
	Jordan Glover <>, Greg KH <>, 
	Petr Mladek <>, Joe Perches <>, Ian Campbell <>, 
	Sergey Senozhatsky <>, Catalin Marinas <>, 
	Will Deacon <>, Steven Rostedt <>, 
	Chris Fries <>, Dave Weinstein <>, 
	Daniel Micay <>, Djalal Harouni <>, 
	Linux Kernel Mailing List <>, Network Development <>, 
	David Miller <>
Subject: Re: Re: [PATCH v4] scripts: add

On Mon, Nov 13, 2017 at 10:05 AM, Tobin C. Harding <> wrote:
> On Mon, Nov 13, 2017 at 06:37:28AM +0300, Kirill A. Shutemov wrote:
>> On Mon, Nov 13, 2017 at 10:06:46AM +1100, Tobin C. Harding wrote:
>> > On Sun, Nov 12, 2017 at 02:10:07AM +0300, Kirill A. Shutemov wrote:
>> >
>> > Thanks for the link. So it looks like we need to refactor the kernel
>> > address regular expression into a function that takes into account the
>> > machine architecture and the number of page table levels. We will need
>> > to add this to the false positive checks also.
>> >
>> > > Not sure if we care. It won't work too for other 64-bit architectrues that
>> > > have more than 256TB of virtual address space.
>> >
>> > Is this because of the virtual memory map?
>> On x86 direct mapping is the nearest thing we have to userspace.
>> > Did you mean 512TB?
>> No, I mean 256TB.
>> You have all kernel memory in the range from 0xffff000000000000 to
>> 0xffffffffffffffff if you have 256 TB of virtual address space. If you
>> hvae more, some thing might be ouside the range.
> Doesn't 4-level paging already limit a system to 64TB of memory? So any
> system better equipped than this will use 5-level paging right? If I am
> totally talking rubbish please ignore, I'm appreciative that you pointed
> out the limitation already. Perhaps we can add a comment to the script
> # Script may miss some addresses on machines with more than 256TB of
> # memory.

I think the 256TB is wrt *virtual* address space not physical RAM.

Also, IMHO, the script should 'transparently' take into account the # of paging
levels (instead of the user needing to pass a parameter).
IOW it should be able to detect the same (say, from the .config file) and act
accordingly - in the sense, the regex's and associated logic would accordingly

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