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

> 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.

afaict, the qemu ring works this way, and sits right next to the store
shared page. So PV guest drivers can get to the qemu ring. I guess no one
is concerned because the worst that could happen is DoS for the naughty
guest. Same with these paging rings.

What I will try to do is call decrease_reservation on the ring pfn once
it's mapped. That way the guest won't have access to it, but the ring will
live due to references from both Xen and the dom0 helper.

I would send that as a follow-up patch though. I think the interface is ok
as is. And if decrease_reservation solves the naughty guest problem, then
that should probably go into qemu as well.

> But that sounds like a good idea all the same.
> Tim.

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