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Re: [Xen-devel] [PATCH] xen: do not unmask disabled IRQ on eoi.

To: "Stefano Stabellini" <stefano.stabellini@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] xen: do not unmask disabled IRQ on eoi.
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Tue, 19 Oct 2010 08:13:16 +0100
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "jeremy@xxxxxxxx" <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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>>> On 18.10.10 at 22:04, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> 
>>> wrote:
> Actually it has just occurred to me that we can safely have clear_evtchn in
> do_upcall and at the same time not mask the evtchn because we are
> protected against executing multiple upcalls at the same time anyway by
> xed_nesting_count.

I wouldn't suggest doing so - while this protects against recursion
for the actual handlers, you may still get do_upcall() invoked way too
many times, up to allowing a guest to continuously trigger an event
making do_upcall() get continuously invoked (as long as event
delivery isn't disabled altogether) - the very situation Ian's patch
you're suggesting to revert tried to address.


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