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Re: [Xen-devel] do_iret bug in xen
- To: "Daniel Stodden" <stodden@xxxxxxxxxx>
- From: "Ashish Bijlani" <ashish.bijlani@xxxxxxxxx>
- Date: Tue, 27 Nov 2007 14:28:20 -0500
- Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 27 Nov 2007 11:29:01 -0800
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- List-id: Xen developer discussion <xen-devel.lists.xensource.com>
since "sti" is on, an interrupt can occur which can cause the control to enter "__runq_tickle", which then invokes "cpumask_raise_softirq(mask, SCHEDULE_SOFTIRQ)" to send IPI to a processor causing the control to enter "__enter_scheduler" which changes the current.
On Nov 27, 2007 2:16 PM, Daniel Stodden < stodden@xxxxxxxxxx> wrote:
On Tue, 2007-11-27 at 13:59 -0500, Ashish Bijlani wrote:
> "do_iret" (slow iret via hyercall) can introduce a race condition as
> "current" can change during the execution of the function. all
> hypercalls run with "sti" on, so an interrupt on a processor causing
> the control to enter in "__enter_scheduler" after reading current can
> change the current process on that processor.
follow the code e.g. surounding ret_from_intr. __enter_scheduler is a
softirq handler. it will only be run upon return to guest context, not
when returning to an interrupted hypervisor. xen is not preemptible.
regards,
daniel
--
Daniel Stodden
LRR - Lehrstuhl für Rechnertechnik und Rechnerorganisation
Institut für Informatik der TU München D-85748 Garching
http://www.lrr.in.tum.de/~stodden mailto:stodden@xxxxxxxxxx
PGP Fingerprint: F5A4 1575 4C56 E26A 0B33 3D80 457E 82AE B0D8 735B
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