Re: [PATCH v4 0/6] virtio core DMA API conversion

From: Andy Lutomirski
Date: Tue Nov 10 2015 - 18:44:40 EST

On Tue, Nov 10, 2015 at 2:27 PM, Benjamin Herrenschmidt
<benh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 2015-11-10 at 10:54 -0800, Andy Lutomirski wrote:
>> Does that work on powerpc on existing kernels?
>> Anyway, here's another crazy idea: make the quirk assume that the
>> IOMMU is bypasses if and only if the weak barriers bit is set on
>> systems that are missing the new DT binding.
> "New DT bindings" doesn't mean much ... how do we change DT bindings on
> existing machines with a FW in flash ?
> What about partition <-> partition virtio such as what we could do on
> PAPR systems. That would have the weak barrier bit.

Is it partition <-> partition, bypassing IOMMU?

I think I'd settle for just something that doesn't regress
non-experimental setups that actually work today and that allow new
setups (x86 with fixed QEMU and maybe something more complicated on
powerpc and/or sparc) to work in all cases.

We could certainly just make powerpc and sparc continue bypassing the
IOMMU until someone comes up with a way to fix it. I'll send out some
patches that do that, and maybe that'll help this make progress.

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