Re: [PATCH 1/2] mm: move force_dma_unencrypted() to mem_encrypt.h

From: Christian Borntraeger
Date: Thu Feb 20 2020 - 12:00:17 EST

On 20.02.20 17:31, Christoph Hellwig wrote:
> On Thu, Feb 20, 2020 at 05:23:20PM +0100, Christian Borntraeger wrote:
>> >From a users perspective it makes absolutely perfect sense to use the
>> bounce buffers when they are NEEDED.
>> Forcing the user to specify iommu_platform just because you need bounce buffers
>> really feels wrong. And obviously we have a severe performance issue
>> because of the indirections.
> The point is that the user should not have to specify iommu_platform.

I (and Halil) agree on that. From a user perspective we want to
have the right thing in the guest without any command option. The iommu_plaform
thing was indeed a first step to make things work.

I might mis-read Halils patch, but isnt one effect of this patch set
that things WILL work without iommu_platform?

> We need to make sure any new hypervisor (especially one that might require
> bounce buffering) always sets it, as was a rather bogus legacy hack
> that isn't extensibe for cases that for example require bounce buffering.