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Re: [Xen-devel] Question about evtchn_callback reentry

To: "Xu, Anthony" <anthony.xu@xxxxxxxxx>, Keir Fraser <keir@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Question about evtchn_callback reentry
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Wed, 20 Dec 2006 10:31:34 +0000
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, xen-ia64-devel <xen-ia64-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Question about evtchn_callback reentry
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On 20/12/06 10:08, "Xu, Anthony" <anthony.xu@xxxxxxxxx> wrote:

> There is no other code operating the global_event_mask.
> Global_event_mask is initiated to 0(unmask).
> Only global_event_mask is 0 and vcpu->vcpu_info->evtchn_upcall_mask is 0,
> Can XEN injects to event_callback_handler of dom0.

How much does injecting a stack frame on ia64 actually cost? It sounds like
it must be quite hideously expensive... I would be inclined to implement
this for x86 by adding the nesting detection into the callback handler
(i.e., the extra callback injection would not be avoided). Keeps the
hypervisor interface clean.

 -- Keir

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