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

From: Benjamin Herrenschmidt
Date: Tue Nov 10 2015 - 19:45:50 EST

On Tue, 2015-11-10 at 15:44 -0800, Andy Lutomirski wrote:
> > 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.

But we haven't found a solution that works. All we have come up with is
a quirk that will force bypass on virtio always and will not allow us
to operate non-bypassing devices on either of those architectures in
the future.

I'm not too happy about this.


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