Re: [Xen-devel] [PATCH 3 of 7] Use a reserved pfn in the guest address space to store mem event rings

[Tim Deegan <tim@xxxxxxx>]

At 08:30 -0800 on 01 Mar (1330590637), Andres Lagar-Cavilla wrote:
> > At 07:47 +0000 on 01 Mar (1330588073), Ian Campbell wrote:
> >> > > Is there no scope for making these pages owned by the domain but not
> >> > > actually part of the P2M? We can cope with that for other types of
> >> magic
> >> > > page, can't we?
> >
> > It would need a new operation to map the ring into the tool that uses
> > it; normal map-foreign-page ops need a GFN.
> 
> Actually, confirmed: we can call xc_domain_decrease_reservation on the
> ring after it's mapped by the helper. Guest won't get at it. Nothing
> breaks.

But that would only work if:
 - the helper always attaches before the guest gets to run; and
 - you never need to restart the helper. 

Tim.

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