linux-kernel - Re: 2.6.25-rc1 xen pvops regression

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Date:	Sat, 16 Feb 2008 22:46:23 +1100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Jody Belka <lists-lkml@...b.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ian Campbell <ijc@...lion.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andi Kleen <andi@...stfloor.org>,
	Mika Penttila <mika.penttila@...umbus.fi>
Subject: Re: 2.6.25-rc1 xen pvops regression

Joel Becker wrote:
> On Sat, Feb 16, 2008 at 01:44:26PM +1100, Jeremy Fitzhardinge wrote:
>   
>> Joel Becker wrote:
>>
>>     
>>> (XEN) mm.c:1825:d109 Bad type (saw 0000000028000001 != exp 
>>> 00000000e0000000) for mfn 3a2f0f (pfn f0)
>>> (XEN) mm.c:649:d109 Error getting mfn 3a2f0f (pfn f0) from L1 entry 
>>> 00000003a2f0f063 for dom109
>>> (XEN) mm.c:1825:d109 Bad type (saw 0000000028000001 != exp 
>>> 00000000e0000000) for mfn 3a2f0f (pfn f0)
>>> (XEN) mm.c:649:d109 Error getting mfn 3a2f0f (pfn f0) from L1 entry 
>>> 00000003a2f0f063 for dom109
>>> (XEN) mm.c:3331:d109 ptwr_emulate: could not get_page_from_l1e()
>>>   
>>>       
>> Hm, I have a suspicion about what this might be.  I'll haven't tried 
>> reproducing it yet though.
>>
>>     
>>> (XEN) Unhandled page fault in domain 109 on VCPU 0 (ec=0003)
>>> (XEN) Pagetable walk from 00000000c01687f0:
>>> (XEN)  L4[0x000] = 00000003a2933027 00000000000006cc
>>> (XEN)  L3[0x003] = 000000039afea027 0000000000000005
>>> (XEN)  L2[0x000] = 000000039bfb7067 0000000000001048 (XEN)  L1[0x168] = 
>>> 00000003a2e97061 0000000000000168
>>> (XEN) domain_crash_sync called from entry.S
>>> (XEN) Domain 109 (vcpu#0) crashed on cpu#2:
>>> (XEN) ----[ Xen-3.1.3-rc3  x86_64  debug=n  Not tainted ]----
>>> (XEN) CPU:    2
>>> (XEN) RIP:    e019:[<00000000c04040bd>]
>>>   
>>>       
>> What does this EIP correspond to in your kernel?  Also:
>>
>> c01687f0 c0417ab6 c040288f c040299a c0403270
>>
>> (as guesses of potential callers to try and work out a stack trace).
>>     
>
> 	ksymoops is no help at all, but I got these from objdump of
> vmlinux:
>
> c04040bd xen_set_pte
> c0417ab6 set_pte_present
> c040288f set_bit
> c040299a __raw_spin_unlock
> c0403270 __set_64bit

(My usual technique is use "gdb vmlinux" and "x/i 0x...." to do the 
lookup.) 

Unfortunately that doesn't narrow down what the kernel was actually 
trying to do at the time.  Clearly a set_pte; looks like someone is 
trying to create a writable mapping of an existing pte page.

Does "console=hvc0 earlyprintk=xen" on the kernel command line give any 
clue about how far it gets before crashing?

    J
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