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Re: [Xen-devel] Failed to access register with invalid access size alignment

  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: "Zytaruk, Kelly" <Kelly.Zytaruk@xxxxxxx>
  • Date: Thu, 10 Apr 2014 14:06:57 +0000
  • Accept-language: en-US
  • Cc: "Xen-devel@xxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxx>
  • Delivery-date: Thu, 10 Apr 2014 14:07:25 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>
  • Thread-index: Ac9Opoupy07MovPYRzKc1uEI6nkmAQAk16oAAAByFMABMxg3QAAI2nUAACZwgJA=
  • Thread-topic: [Xen-devel] Failed to access register with invalid access size alignment

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Wednesday, April 09, 2014 11:40 AM
> To: Zytaruk, Kelly
> Cc: Xen-devel@xxxxxxxxxxxxx
> Subject: RE: [Xen-devel] Failed to access register with invalid access size
> alignment
> >>> On 09.04.14 at 17:32, <Kelly.Zytaruk@xxxxxxx> wrote:
> >> > Did you manage to find out where the bad request originates, and
> >> > how it behaves when run on bare hardware?
> >>
> >
> > Using Xenctx (thanks Konrad ) I have managed to determine that the
> > access is coming from a call to "hal!READ_PORT_ULONG" in the Win7
> > guest.  This is the guest OS that is making the request.
> Which, I'm afraid, means that we'll have to allow the access in one way or
> another (up to and including the current model, as I then would conclude this
> isn't causing any actual problem - iirc you merely tried to understand 
> whether it
> would).

In this specific case it doesn't appear to be the root of my problem (back to 
the drawing board).  I am passing through two PCI devices; a graphics adapter 
and a 1394 firewire adapter.  It only does the mis-aligned access for the 
graphics adapter.  The 1394 appears not to have any problem.

This is happening long before the graphics driver is loaded in the guest.  In 
this specific case it does not cause as issue (assuming that it is relying only 
the header type).  For the case of the graphics adapter the header type is '0' 
which is the default that QEMU returns when it sees the invalid alignment 
access, so no problem here.  If however the alignment problem occurred with a 
type 1 header then there would be a problem.  But I really don't know what is 
causing Win7 to treat the graphics adapter differently so it is hard to say 
whether or not this would occur under different scenarios.


> Jan

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