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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 10/04/14 15:06, Zytaruk, Kelly wrote:
>
>> -----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.
>
> Kelly

What is the class code of the graphics adapter, and which virtual
display is qemu creating for the domain?

We have seen issues with cards in the past where the class code was
"Other". Win7 saw an emulated cirrus display, decided it was the most
capable real display adapter, loaded its legacy graphics driver stack
and was unable to subsequently load the non-legacy driver for the
"Other" card.

~Andrew

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