linux-kernel - Re: Kexec query about what makes sure control pages/page tables are not overwritten

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Date:	Mon, 11 Nov 2013 16:14:51 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: Kexec query about what makes sure control pages/page tables are
 not overwritten

On Mon, Nov 11, 2013 at 12:57:12PM -0800, H. Peter Anvin wrote:
> It is pretty simple: the kernel exports how much text+data+bss+brk it needs, and the kernel cannot use memory outside that region until it is ready to control the address space itself.

Ok. So looks like that field is.

0260/4  2.10+   init_size       Linear memory required during initialization

This helps. Thanks.

Vivek

>
 
> Vivek Goyal <vgoyal@...hat.com> wrote:
> >Hi,
> >
> >I am staring at control page allocation logic in case of kdump and
> >wondering what makes sure that these pages are not overwritten by 
> >next kernel.
> >
> >I see that for 64bit entry, control pages have the page tables needed
> >for second kernel. In case of crash these pages from from crash kernel
> >reserved region. Page allocator is very simple and that is start from
> >lowest crash reserved range and move higher and allocate first
> >available
> >page which is not allocated to segments. What makes sure that these
> >pages
> >are not overwritten by second kernel.
> >
> >I guess it becomes a general bootloader question. How do we make sure
> >bootloader prepared page tables/gdt will not be overwritten by kernel
> >(till kernel sets up its own page tables and gdt) and how should we do
> >the
> >allocation and placement.
> >
> >Thanks
> >Vivek
> 
> -- 
> Sent from my mobile phone.  Please pardon brevity and lack of formatting.
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