Re: Debugging KVM

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

Barry Silverman wrote:
> I am curious what techniques are being used to debug problems with KVM.
>
> Are you using the qemu GDB stub to step the guest, or using KDB/KGDB to debug
> the driver-level code, or just using a kernel printfs?
>
>   

Various techniques are used depending on the bug and the weather.  If a 
guest won't boot, I dump a list of visited instruction pointers from 
qemu and do a binary search on that using the kvm hardware breakpoint 
feature.  If the guest is Linux, you can modify it to check itself 
mode.  For mmu trouble, sometimes enabling AUDIT in mmu.c helps; 
sometimes I have to add a test for a specific misbehaving address.  For 
host crashes, printks+netconsole are the way (though a kernel debugger 
might help here; I'm just used to printks).


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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