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


  • To: Christoph Egger <Christoph.Egger@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir@xxxxxxxxxxxxx>
  • Date: Thu, 09 Aug 2007 09:44:41 +0100
  • Delivery-date: Thu, 09 Aug 2007 01:42:31 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcfaYYa0xVa1iUZUEdyJlwAX8io7RQ==
  • Thread-topic: [Xen-devel] [PATCH] Fix races in iret hypercall

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
only.

How did you conclude there was a bug?

 -- Keir


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