Re: mmiotrace bug: recursive probe hit

[Avi Kivity]

Pekka Enberg wrote:
> On Sat, Apr 5, 2008 at 10:36 AM, Avi Kivity <avi@xxxxxxxxxxxx> wrote:
>   
> > It should not be too difficult to modify x86_emulate.c to do everything
> > through a function vector.  However there is a simpler (for you) solution:
> > run the driver-to-be-reverse-engineered in a kvm guest, and modify kvm
> > userspace to log accesses to mmio regions.  This requires the not-yet-merged
> > pci passthrough support.  You can reverse engineer Windows drivers with this
> > as well.
> >
> >  This won't work for kmemcheck smp though.
> >     
>
> For kmemcheck, I'd prefer the per-CPU page tables suggested by Ingo.
> I'm having hard time understanding why that's a "ugly hack" compared
> to using kvm for this...
>   

It's not an ugly hack, but will be very very difficult.  With mmu 
notifiers it's probably doable though:

- the linux page tables are never loaded into cr3, but rather kept as a 
reference
- page faults are by instantiating ptes into shadow page tables (which 
track the linux page tables)
- mmu notifiers are used to drop shadow ptes when the linux ptes change

--
Any sufficiently difficult bug is indistinguishable from a feature.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/