Re: [patch] kvm: make cr3 loading more robust

[Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>]

* Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:

> >rmap_write_protect() has a BUG_ON() if a physical address is not 
> >found the the memslot. But this is a possible scenario if a buggy 
> >guest OS loads an invalid or corrupted cr3 value. So exit more 
> >gracefully.
> 
> I think a better solution is to detect the invalid cr3 in new_cr3(). 
> That way the entire chain of error returns is avoided.

i'm wondering what the right semantics would be though. Kill the VM 
context?

on a real CPU an invalid cr3 does nothing explicitly (besides being a 
sure way to get a triple fault) - physical memory is always accessible, 
non-present physical memory at most generates an #MCE, but is typically 
just returning 0xff, right? So perhaps keep a non-mapped page filled 
with 0xff and map non-existent RAM to that? But then this 'RAM' needs to 
be made non-writable. Looks a bit messy. Cleanest would be to kill the 
VM context (without injecting any fault into the guest), but that would 
then require an error return chain from set_cr3() ...

	Ingo

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