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

[Jan Kiszka <jan.kiszka@xxxxxxxxxxx>]

On 2015-07-28 19:15, Paolo Bonzini wrote:
> 
> 
> 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.

Yes, it's practically working, but it's not accurate /wrt how that
hardware looked like in reality.

> 
> 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.

Great!

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux

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