linux-kernel - Re: BUG: unable to handle kernel paging request at ffffc7ff81000398 (sys_kexec

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Date:	Sun, 22 Jan 2012 02:18:45 -0500
From:	Sasha Levin <levinsasha928@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Dave Jones <davej@...hat.com>, kexec@...ts.infradead.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: BUG: unable to handle kernel paging request at ffffc7ff81000398
 (sys_kexec_load)

On Sat, 2012-01-21 at 20:49 -0800, Eric W. Biederman wrote:
> Sasha Levin <levinsasha928@...il.com> writes:
> 
> > Hi All,
> >
> > I got the following BUG() while running trinity within KVM tool.
> >
> > It looks like the result of a kexec_load(), but I couldn't find any
> > mention of it in the logs - which is strange since logs are supposed
> > to be flushed before actual syscall runs.
> 
> Interesting.
> 
> The fact that this happens in native_set_pte would suggest that we are
> trying to write to a page table that does not exist.  So this might
> be a layer below kexec_load that has the problem.
> 
> Do you have the kernel you were testing?    A disassembly of the
> native_set_pte, machine_kexec_prepare and sys_kexec_load
> would be interesting, for attempting to trace this back to what went
> wrong.

Yup, It's a pretty simple build of linux-next from today.

>From what I gather, native_set_pte is a simple short function, it also
gets inlined so the disassembly is pretty trivial. I've attached
disassembly of other two functions.

-- 

Sasha.

View attachment "disasm.txt" of type "text/plain" (43075 bytes)