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Re: [Xen-devel] [PATCH] x86: clear guest's EFLAGS.RF after emulating instructions


  • To: Jan Beulich <jbeulich@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Tue, 19 Jun 2007 11:19:51 +0100
  • Delivery-date: Tue, 19 Jun 2007 03:17:56 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AceyW18PnaV/jh5OEdyOfAAX8io7RQ==
  • Thread-topic: [Xen-devel] [PATCH] x86: clear guest's EFLAGS.RF after emulating instructions

On 19/6/07 11:09, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> You set EFLAGS.RF in a few places when injecting #PF. Why would you do that?
>> It isn't Xen's job to set that flag ever afaics, and since the original trap
>> into Xen was not due to #DB you're not avoiding an infinite loop.
> 
> This is only in handle_mmio() where I cleared the flag earlier - since #PF has
> lower
> priority than #DB, .RF must have been set when the exception was reported, and
> hence I must re-set it when forwarding the exception.

Oh, I see. I'm not too familiar with #DB or EFLAGS.RF, but this does appear
to make sense given the info in the reference manual.

 -- Keir



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