Re: [Xen-devel] [PATCH v6 08/14] vtd: add lookup_page method to iommu_ops

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.09.18 at 17:24, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 07 September 2018 15:56
>> 
>> >>> On 07.09.18 at 14:36, <Paul.Durrant@xxxxxxxxxx> wrote:
>> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> >> Sent: 07 September 2018 12:11
>> >>
>> >> >>> On 23.08.18 at 11:47, <paul.durrant@xxxxxxxxxx> wrote:
>> >> > This patch adds a new method to the VT-d IOMMU implementation to
>> find
>> >> the
>> >> > MFN currently mapped by the specified BFN along with a wrapper
>> function
>> >> in
>> >> > generic IOMMU code to call the implementation if it exists.
>> >>
>> >> For this to go in, I think the AMD side of it wants to also be 
>> >> implemented.
>> >
>> > Why? It can be done later. Nothing existing is going to break if it is not
>> > implemented.
>> 
>> If it was something that's terribly difficult to implement, I'd
>> probably agree. But introducing PV IOMMU for Intel only (and
>> hence once again making AMD a second class citizen) I don't
>> really like. Another thing would be if you had the implementation
>> ready, but the maintainer(s) don't respond...
>> 
> 
> It's all time though. The fact is that, in XenServer, we've never had 
> PV-IOMMU for AMD. It would be wonderful to have it for AMD too and indeed I 
> may find the time to do it, but is that really a reason to block integration 
> of these patches when no actual regression will be caused by of the lack of 
> AMD support?

First of all - I don't mean to block anything. I deliberately said
"I think it wants to be", not "It needs to be". But beyond that
my second class citizen statement stands - it's no different
from e.g. introducing VMX support, but not SVM one. That also
is not resulting in any regression, but still is not very desirable.

Jan



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