Re: [Xen-devel] [PATCH] xenpaging:close domU's event channel and free port

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-02-15 at 02:24 +0000, Hongkaixing wrote:
> 
> > -----Original Message-----
> > From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx]
> > Perhaps I'm misunderstanding something and/or showing my ignorance about
> > how xenpaging works but why does paging need a domU event channel
> > anyway? Surely paging is transparent to the guest.
> > 
> > Or is this really a dom0<->Xen event channel which just appears to be
> > assigned to the guest?
> 
> In xenpaging source code, there is an inter-domain event channel between dom0 
> and domU.
[...]
> > Who assigns this remote domain port? Shouldn't it either be closed when
> > the dom0 end is closed or retained such that it can be reused each time
> > instead of leaking?
> 
>   In mem_event_enable(), the function alloc_unbound_xen_event_channel() 
> allocates a free port for domU,
> and assigns to xen_consumer;When xenpaging tears down, it just frees dom0's 
> event channel port by xc_evtchn_unbind(),
> leaves domU's port still occupied. So we should add the patch to free domU's 
> port when xenpaging exits.

The two ends of that event channel are actually dom0 and Xen, because
chn->xen_consumer is not NULL, even though the Xen end does live in the
domU evtchn address space. It is not exactly dom0 and domU as you
suggest, which is where my confused question arose.

Ian.


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