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Re: [Xen-devel] Question: dom0 electrocuted by implicitly unmapped grant

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Question: dom0 electrocuted by implicitly unmapped grantrefs
From: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Date: Mon, 23 Nov 2009 15:07:26 -0800
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On Mon, 2009-11-23 at 17:52 -0500, Keir Fraser wrote:
> On 23/11/2009 22:43, "Daniel Stodden" <daniel.stodden@xxxxxxxxxx> wrote:
> > I assume 'implicitly unmapped' therein refers to a case where rd is gone
> > because ld in some or the other way already managed to tear down a
> > mapping without an exlicit gnttab call? This correct? Otherwise killing
> > ld would seem a bit rough to me :}
> You are correct.
> > Either way: is domain_crash(ld) the appropriate response? Why not just
> > fail the op and let the caller live and learn?
> It's arguable I suppose. An implicitly unmapped grant leaves a grant entry
> which cannot be released until the mapping domain dies. It's a nasty kind of
> leak, and I made the hypervisor's response to it suitably abrupt.

Forgive my ignorance: Why can't it be released any more? To me it looks
as if the mapping is already gone, so the entry is stale, and the caller
just pointed at it somewhat asking for just that.


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