Linux Virtualization - Nov 2015 - [PATCH v4 0/6] virtio core DMA API conversion

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.

Ben.

On Nov 10, 2015 4:44 PM, "Benjamin Herrenschmidt"
<benh at kernel.crashing.org> 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.

--Andy

On Tue, 2015-11-10 at 20:46 -0800, Andy Lutomirski
wrote:
> 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.
Ok, give me a few days for my headache & fever to subside see if I can
find something better. David, no idea from your side ? :-)

Cheers,
Ben.