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

Alexey Kardashevskiy aik at
Fri Jul 19 18:23:59 AEST 2019

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 

>>> 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.


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