Re: [PATCH v2 1/4] x86/mm: Export force_dma_unencrypted

[Christoph Hellwig]

On Wed, Sep 04, 2019 at 09:32:30AM +0200, Thomas Hellström (VMware) wrote:
> That sounds great. Is there anything I can do to help out? I thought this
> was more or less a dead end since the current dma_mmap_ API requires the
> mmap_sem to be held in write mode (modifying the vma->vm_flags) whereas
> fault() only offers read mode. But that would definitely work.

We'll just need to split into a setup and faul phase.  I have some
sketches from a while ago, let me dust them off so that you can
try them.

> "If it's the latter, then I would like to reiterate that it would be better
> that we work to come up with a long term plan to add what's missing to the
> DMA api to help graphics drivers use coherent memory?"

I don't think we need a long term plan.  We've been adding features
on an as-needed basis.  And now that we have siginificanty less
implementations of the API this actually becomes much easier as well.