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

Ingo Molnar
2007-01-03T11:52:30Z

* 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