Re: PCI-passthrough for 32 bit guests and high MMIO addresses

[David Vrabel <david.vrabel@citrix.com>]

On 21/11/14 16:00, Jan Beulich wrote:
>>>> On 21.11.14 at 16:48, <david.vrabel@citrix.com> wrote:
>> On 21/11/14 15:38, Jan Beulich wrote:
>>>>>> On 21.11.14 at 16:01, <andrew.cooper3@citrix.com> wrote:
>>>> On 21/11/14 14:54, Jan Beulich wrote:
>>>>>>>> On 21.11.14 at 15:39, <JGross@suse.com> wrote:
>>>>>> Trying to do PCI-passthrough with a 32-bit pv-domain I passed the
>>>>>> wrong device to the domain. The MMIO address was too large for a
>>>>>> MFN of a 32-bit system (it was 380003200000-3800036fffff).
>>>>>>
>>>>>> Instead of rejecting the operation Xen tried to perform it resulting
>>>>>> in a (quite understandable) failure in the domU.
>>>>>>
>>>>>> I think either the hypervisor or the tools should refuse to do
>>>>>> PCI-passthrough in this case.
>>>>> What's wrong with this large an address?
>>>>
>>>> It is wider than 44 bits, so doesn't fit in a 32bit pfn for p2m/m2p
>>>> update operations.
>>>
>>> MMIO regions don't go into these tables.
>>
>> They do in upstream kernels.
> 
> Which still is no reason to make the hypervisor or tools refuse
> anything here. A check like the one Jürgen is asking for should
> be added only if something in the public interface prevents this
> from working; everything beyond should be dealt with by the
> respective kernel.

I agree.

David

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