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

[Alexey Kardashevskiy]

On 19/07/2019 18:05, Christoph Hellwig wrote:
> On Fri, Jul 19, 2019 at 06:00:25PM +1000, Alexey Kardashevskiy wrote:
>>> 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.
> 
> Well, I mean as in literally not setting a dma_ops so that the
> dma_direct code is used without the indirection through the iommu ops.
> This is not only more obvious, but also faster as you avoid the
> indirect call (although that probably doesn't matter much if you
> are bounce buffering anyway).

I was not precise. We cannot avoid IOMMU in the guest for passed through 
devices.


>>> Also isn't that support non-upstream so far?
>>
>> How is this relevant? I expect the existing "swiotlb=force" just work.
> 
> I though the whole secure VM support was still not upstream.

It is getting there and I still do not see why "swiotlb=force" should 
not work if chosed in the cmdline.


-- 
Alexey