question on "powerpc/pseries/dma: Allow SWIOTLB"

[Alexey Kardashevskiy]

On 19/07/2019 17:53, Christoph Hellwig wrote:
> On Fri, Jul 19, 2019 at 05:52:37PM +1000, Alexey Kardashevskiy wrote:
>>
>>
>> On 19/07/2019 17:10, Christoph Hellwig wrote:
>>> Hey Alexey,
>>>
>>> what is the use case for the above commit?  Shouldn't we handle all
>>> addressing limits using the iommu?
>>
>> Our secure VMs is the use case, when only a fraction of system memory is
>> available for DMA.
> 
> But shouldn't we force usage of the direct ops in that case as the
> IOMMU is not neededed at all?

We do, for mappings, but not unmappings and syncing.

> Also isn't that support non-upstream so far?

How is this relevant? I expect the existing "swiotlb=force" just work.


-- 
Alexey