From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH 2/2] xen/gnt{dev,
	alloc}: reserve event channels for notify
Date: Tue, 25 Oct 2011 15:51:56 -0400
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> That same SELinux category-based isolation mechanism is also a good solution for xen
> qemu-dm processes, although moving qemu to a stubdom provides better isolation since
> SELinux currently cannot talk to XSM to determine what domains a particular qemu-dm 
> process should be able to manipulate.

<nods>
> 
> Only allowing event channels allocated by userspace to be used in gnt* notify is
> a good idea, since there's no reason for userspace to need to manipulate an event
> channel set up by the kernel.
> 
.. snip..
> > 
> > How would that work when the IRQ subsystem (so everything is setup in the kernel)
> > gets an event? Would the refcount be for that -1.. oh. You would only set
> > the refcnt when the _get/_put calls are made and not when in-kernel calls to setup
> > IRQs are done?
> > 
> 
> Right. The reference count would be a dual-purpose field indicating if the event
> channel is kernel-internal (value -1) or userspace-visible (reference count > 0).
> New event channels would start out at -1, and evtchn.c would change them to 1.

The tricky bit is going to be with the xen_free_irq which might have to deal with kernel
events and grantdev events... oh wait, the event_put is going to decrement it and then
call xen_free_irq, so that will come out to be the right number.

Looking forward to the patches! Thanks for doing this work.