Xen devel - Feb 2006 - implicit grant unmap

Hello All,
I''m contemplating ways to avoid the domain_crash() in mm.c line ~615
without requiring new OS hooks.  This crash occurs when the operating
system writes a zero to the PTE for a grant mapping without an explicit
Xen call to unmap.

In hacking around, it seems the problem is this:  When the mapping PTE
gets squashed, Xen''s cleanup_writable_pagetable() has no way to find
the
correct maptrack entry for the affected mapping.  Consequently, the
grant mapping is not properly cleaned-up.

Sound correct?  Are there worse problems here?

Thanks,
-steve

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On 14 Feb 2006, at 21:07, King, Steven R wrote:
> I''m contemplating ways to avoid the domain_crash() in mm.c line
~615
> without requiring new OS hooks.  This crash occurs when the operating
> system writes a zero to the PTE for a grant mapping without an explicit
> Xen call to unmap.
>
> In hacking around, it seems the problem is this:  When the mapping PTE
> gets squashed, Xen''s cleanup_writable_pagetable() has no way to
find
> the
> correct maptrack entry for the affected mapping.  Consequently, the
> grant mapping is not properly cleaned-up.
>
> Sound correct?  Are there worse problems here?
That''s right. That grant will hang around until the domain is 
destroyed, at which point the grant is cleaned up by 
gnttab_release_mappings().

  -- Keir


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