Re: [Xen-devel] Xen 4.7 crash

[Aaron Cornelius <Aaron.Cornelius@xxxxxxxxxxxxxxx>]

> -----Original Message-----
> From: Andrew Cooper [mailto:amc96@xxxxxxxxxxxxxxxx] On Behalf Of
> Andrew Cooper
> Sent: Wednesday, June 1, 2016 4:01 PM
> To: Aaron Cornelius <Aaron.Cornelius@xxxxxxxxxxxxxxx>; Xen-devel <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>
> Subject: Re: [Xen-devel] Xen 4.7 crash
> 
> On 01/06/2016 20:54, Aaron Cornelius wrote:
> > I am doing some work with Xen 4.7 on the cubietruck (ARM32).  I've
> noticed some strange behavior after I create/destroy enough domains and
> put together a script to do the add/remove for me.  For this particular test I
> am creating a small mini-os (Mirage) domain with 32MB of RAM, deleting it,
> creating the new one, and so on.
> >
> > After running this for a while, I get the following error (with version
> 8478c9409a2c6726208e8dbc9f3e455b76725a33):
> >
> > (d846) Virtual -> physical offset = 3fc00000
> > (d846) Checking DTB at 023ff000...
> > (d846) [32;1mMirageOS booting...[0m
> > (d846) Initialising console ... done.
> > (d846) gnttab_stubs.c: initialised mini-os gntmap
> > (d846) allocate_ondemand(1, 1) returning 2300000
> > (d846) allocate_ondemand(1, 1) returning 2301000
> > (XEN) grant_table.c:3288:d0v1 Grant release (0) ref:(9) flags:(2)
> > dom:(0)
> > (XEN) grant_table.c:3288:d0v1 Grant release (1) ref:(11) flags:(2)
> > dom:(0)
> > (XEN) p2m.c: dom1101: VMID pool exhausted
> > (XEN) CPU0: Unexpected Trap: Data Abort <snip>
> >
> > I'm not 100% sure, from the "VMID pool exhausted" message it would
> appear that the p2m_init() function failed to allocate a VM ID, which caused
> domain creation to fail, and the NULL pointer dereference when trying to
> clean up the not-fully-created domain.
> >
> > However, since I only have 1 domain active at a time, I'm not sure why I
> should run out of VM IDs.
> 
> Sounds like a VMID resource leak.  Check to see whether it is freed properly
> in domain_destroy().
> 
> ~Andrew

That would be my assumption.  But as far as I can tell, arch_domain_destroy() 
calls pwm_teardown() which calls p2m_free_vmid(), and none of the functionality 
related to freeing a VM ID appears to have changed in years.

- Aaron
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