Re: [Xen-devel] [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 28/07/2015 18:42, Jan Kiszka wrote:
> > On the other hand interrupt remapping is absolutely necessary for
> > production use, hence my point that x86 does not promise API stability.
> 
> Well, we currently implement the features that the Q35 used to expose.
> Adding interrupt remapping will require a new chipset and/or a hack
> switch to ignore compatibility.

Isn't the VT-d register space separate from other Q35 features and
backwards-compatible?  You could even add it to PIIX in theory just by
adding a DMAR.

It's not like for example SMRAM, where the registers are in the
northbridge configuration space and move around in every chipset generation.

> > ("Any kind of stability" actually didn't include crashes; those are not
> > expected :))
> > 
> > The Google patches for userspace PIC and IOAPIC are proceeding well, so
> > hopefully we can have interrupt remapping soon.
> 
> If the day had 48 hours... I'd love to look into this, first adding QEMU
> support for the new irqchip architecture.

I hope I can squeeze in some time for that...  Google also had an intern
that was looking at it.

Paolo

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