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Re: [Xen-devel] [PATCH] Fix races in iret hypercall

To: Christoph Egger <Christoph.Egger@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Fix races in iret hypercall
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Thu, 09 Aug 2007 09:44:41 +0100
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Thread-topic: [Xen-devel] [PATCH] Fix races in iret hypercall
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On 9/8/07 09:35, "Christoph Egger" <Christoph.Egger@xxxxxxx> wrote:

> Attached patch fixes races seen on SMP when multiple HVM guests
> execute the iret instruction at the same time.
> current vcpu can change in the middle of do_iret().

This is fine as a cleanup, but it does not fix any bugs!

For two reasons:
 1. Current vcpu *cannot* change in the middle of do_iret(). Xen does not
support involuntary preemption.
 2. HVM guests do not ever execute do_iret(). That function is for pv guests

How did you conclude there was a bug?

 -- Keir

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