Re: [Xen-devel] 15142:78389dbb08bb and domain state

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

Oh dear. Do you map top-level pagetables into each other (i.e., linear
mappings of other page tables)? Then you could have a circular reference
where one level-4 pagetable references the other, and vice versa. But we
though of that and break loops in relinquish_memory() in arch/x86/domain.c.
Perhaps that's broken though -- it's certainly been modified recently to
support linear mappings at lower levels in the pagetable hierarchy.

I would add some tracing to the 'q' key to dump the contents of the
remaining few pages, and see if they actually reference each other. Also
some tracing around relinquish_memory() is probably not a bad idea.

 -- Keir

On 9/11/07 16:06, "John Levon" <levon@xxxxxxxxxxxxxxxxx> wrote:

> Thanks!
> 
> (XEN) Memory pages belonging to domain 1:
> (XEN)     DomPage 000000019ddbf000: mfn=000000000019ddbf, caf=00000001,
> taf=0000000080000001
> (XEN) Memory pages belonging to domain 2:
> (XEN)     DomPage 00000001f4dbc000: mfn=00000000001f4dbc, caf=00000001,
> taf=0000000080000001
> 
> #define PGT_l4_page_table   (4UL<<29) /* using this page as an L4 page table?
> */
> 
> Is it possible we do something unusual, and there's an accounting bug? It
> seems
> that vcpu_destroy_pagetables() should kill any active reference. If I boot
> into
> the kernel debugger (so no userspace) and destroy the domain, it still
> happens.
> 
> Before I try and work up something to track references to the kernel's
> CR3 dompage, any suggestions or ideas?



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