Re: [Xen-devel] [PATCH 2/4] iommu: generalize iommu_inclusive_mapping

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.07.18 at 17:33, <roger.pau@xxxxxxxxxx> wrote:
> On Tue, Jul 31, 2018 at 08:39:22AM -0600, Jan Beulich wrote:
>> >>> On 27.07.18 at 17:31, <roger.pau@xxxxxxxxxx> wrote:
>> > Introduce a new iommu=inclusive generic option that supersedes
>> > iommu_inclusive_mapping. This should be a non-functional change on
>> > Intel hardware, while AMD hardware will gain the same functionality of
>> > mapping almost everything below the 4GB boundary.
>> 
>> So first of all - what's the motivation behind this change? So far we
>> had no need for hacks line the VT-d side one on AMD. I don't think
>> this should be widened without there being indication of a problem
>> with non-niche AMD systems.
> 
> OK, I can leave the default on for Intel and off for everything else,
> but I will introduce the generic dom0-iommu= option anyway.

Hmm, I've always been wishing we'd change to a default of off for
VT-d as well - imo we shouldn't by default assume broken firmware.
Kevin?

As to AMD - you still don't really say why this would be needed
there. I'm not in favor of workarounds when there's nothing to
work around. IOW - if the logic isn't needed on AMD, do we need
this code movement in the first place?

Jan



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