linux-kernel - Re: correction to compat_sys_kexec

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Date:	Fri, 23 May 2008 17:36:26 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Bernhard Walle <bwalle@...e.de>
Cc:	Sharyathi Nagesh <sharyath@...ibm.com>, akpm@...l.org,
	mohd.omar@...ibm.com, IndhuDurai@...ibm.com,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	fastboot@...ts.osdl.org, linux-kernel@...r.kernel.org,
	mohan@...ibm.com, sachinp@...ibm.com
Subject: Re: correction to compat_sys_kexec_load

Bernhard Walle <bwalle@...e.de> writes:

> * ebiederm@...ssion.com (Eric W. Biederman) [2008-05-23 13:14]:
>>
>> What we need to do is fix /sbin/kexec to pass in the correct
>> architecture of the kernel for unload as it does for load.
>
> How should it know that it unloads a 32 bit kernel on a 64 bit system?
> It doesn't have access to the kernel any more once it has been loaded.

The architecture parameter is the architecture of the running kernel
that implements sys_kexec_load.

Because it is a pain for testing and in general impossible we don't
change cpu modes during a kexec.  So a 32bit caller of sys_kexec_load
will need to passing in different code if it is running on a 32bit or
a 64bit kernel.

The trampoline code in /sbin/kexec does change modes on x86 when
appropriate.

Caring if you know the architecture in the unload case is a bit
silly. As there is no real justification for it.  At this
point getting user space fixed so that it works on older kernels
seems important. 

Eric
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