linux-kernel - Re: linux page table

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Date:	Sun, 2 Sep 2012 10:10:41 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Xin Tong <xerox.time.tech@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: linux page table

On Sat, 1 Sep 2012, Xin Tong wrote:

> When a process is created in Linux, corresponding page table is
> implemented. In the current x86 linux, the page table is a multi-level
> page table and CR3 points to the first level of the page table.  I
> have 2 questions.
> 
> 1. is the value in CR3 virtual address or physical address ?

Physical, otherwise you will have chicken-egg problem.

> 2. can the address of the first level of the page table during a
> process's lifetime change ?

In theory it would be possible to implement. But I don't see a scenario 
when it might be useful.

> 3. can two different processes have their CR3 being the same value
> even though they have different first level page tables ?

Yes, if they are created by clone(CLONE_VM). In such case they share the 
same mm_struct, and therefore mm_struct->pgd (which is exactly what is 
loaded into cr3 in switch_mm()) is the same.

LKML is however very inappropriate list for such questions. Please ask on 
kernelnewbies list next time.

-- 
Jiri Kosina
SUSE Labs

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