From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: do_iret bug in xen
Date: Tue, 27 Nov 2007 23:17:16 +0000
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On Tue, 2007-11-27 at 17:41 -0500, Ashish Bijlani wrote:
> "cpumask_raise_softirq(mask, SCHEDULE_SOFTIRQ)" sends an IPI to the
> target processor, this can cause current to change.

No it can't.

The IPI causes smp_event_check_interrupt() to be called which just ACKs
the IPI and returns via ret_from_intr (in entry.S). It is only if a
guest was interrupted that we go down the test_all_events path which
processes softirqs. If it was Xen which was interrupted then we go to
restore_all_xen which just returns to Xen. In this case Xen will
eventually return to the guest and take the test_all_events path and
process the softirq.

Ian.