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

From: Andy Lutomirski
Date: Tue Nov 10 2015 - 23:48:05 EST

On Nov 10, 2015 4:44 PM, "Benjamin Herrenschmidt"
<benh@xxxxxxxxxxxxxxxxxxx> wrote:
> 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?
> No.
> > 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.

Me neither. At least it wouldn't be a regression, but it's still crappy.

I think that arm is fine, at least. I was unable to find an arm QEMU
config that has any problems with my patches.

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