linux-kernel - Re: kernel bug in kvm

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Date:	Sun, 01 Nov 2009 13:31:04 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Andrew Theurer <habanero@...ux.vnet.ibm.com>, kvm@...r.kernel.org,
	Linux-kernel@...r.kernel.org
Subject: Re: kernel bug in kvm_intel

On 11/01/2009 12:45 PM, Tejun Heo wrote:
> Hello,
>
> Avi Kivity wrote:
>    
>> We get a page fault immediately (next instruction) after returning from
>> the guest when running with oprofile.  The page fault address does not
>> match anything the instruction does, so presumably it is one of the
>> accesses the processor performs in order to service an NMI (ordinary
>> interrupts are masked; and the fact that it happens with oprofile
>> strengthens this assumption).
>>      
> Ah... okay, that's tricky but IIRC faults like that can be
> distinguished from regular ones via processor state, right?
>    

Not on x86.  But given that the fault address is different from %rsp 
(which is what the instruction accesses) and %rip, there aren't many 
alternatives.

>> Here is the code in question:
>>
>>      
>>>      3ae7:       75 05                   jne    3aee<vmx_vcpu_run+0x26a>
>>>        3ae9:       0f 01 c2                vmlaunch
>>>        3aec:       eb 03                   jmp    3af1<vmx_vcpu_run+0x26d>
>>>        3aee:       0f 01 c3                vmresume
>>>        3af1:       48 87 0c 24             xchg   %rcx,(%rsp)
>>>        
>> ^^^ fault, but not at (%rsp)
>>      
> Can you please post the full oops (including kernel debug messages
> during boot) or give me a pointer to the original message?

http://www.mail-archive.com/kvm@vger.kernel.org/msg23458.html

> Also, does
> the faulting address coincide with any symbol?
>    

No (at least, not in System.map).

-- 
error compiling committee.c: too many arguments to function

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