Re: BUG_ON in mmu.c:436

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Ryan Harper wrote:
> * Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org> [2007-09-24 16:39]:
>   
>> Ryan Harper wrote:
>>     
>>> * Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> [2007-09-24 02:57]:
>>>  
>>>       
>>>> Ryan Harper wrote:
>>>>    
>>>>         
>>>>> I've run into a nasty bug while trying to install a Linux guest using
>>>>> VMware Server inside a kvm guest (full dmesg attached and recreate
>>>>> instructions below bug).
>>>>>
>>>>>
>>>>>      
>>>>>           
>>>> Can you reproduce this with AUDIT turned on (top of mmu.c)? AUDIT is 
>>>> very slow, so it's recommended to reduce guest memory as much as possible.
>>>>    
>>>>         
>>> Working on it -- running for the better part of today with 256MB and I'm
>>> still booting up the guest.  I'll let you know how things go tomorrow.
>>> Any thoughts on how to speed audit runs up other than lower guest
>>> memory?
>>>  
>>>       
>> savevm right before you're about to launch your test w/o audit enabled.  
>> then launch with loadvm and audit enabled and hit <enter> to launch your 
>> test.
>>     
>
> That was highly effective in getting as close to the fault as possible.
>   

We may want to add a module parameter so that audit can be enabled and 
disabled at runtime when compiled in.

> I ended up removing all callers to kvm_mmu_audit() and added one to
> mmu.c:rmap_write_protect() write before the BUG_ON() fires.  Here is the
> kvm_mmu_audit() output the crash generates:
>
>
> audit_write_protection: (rmap_write_protect()) shadow page has writable mappings: gfn 5297 role 112
> audit_write_protection: (rmap_write_protect()) shadow page has writable mappings: gfn 6d52 role 112
> audit_write_protection: (rmap_write_protect()) shadow page has writable mappings: gfn 659b role 12
>   


We need to bracket the error so that we know exactly where the problem 
starts to appear, and then enable debug (conditionally on rip and/or 
cr2) so that we have a full trace of what happens.


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


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