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Re: [Xen-devel] HVM windows - PCI IRQ firing on both CPU's

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] HVM windows - PCI IRQ firing on both CPU's
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 18 Aug 2008 13:06:49 +0100
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On 18/8/08 11:53, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

> The first number is the timestamp (why is the TSC so far out of whack
> between CPU's??? Is that a hardware thing or a Xen thing? It causes huge
> problems with 'ping' too!!!), the second is the isr that is running.
> Why is the ISR getting run again immediately on the other CPU? Is this
> an OS thing or am I not acking the interrupt correctly?

You should be checking and clearing only vcpu0's evtchn_upcall_pending and
evtchn_pending_sel fields. Other vcpu's equivalent fields are currently
unused for HVM guests. It is essential that you clear evtchn_upcall_pending
-- that is the 'virtual interrupt wire' connected to the virtual PIC's
level-triggered input pin.

Apart from those caveats, all should work fine with no spurious interrupts.

 -- Keir

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