Re: [Qemu-devel] [PATCH 5/5] intel_iommu: do not allow EIM without KVM support

[Peter Xu]

On Fri, Sep 23, 2016 at 12:39:19PM +0200, Paolo Bonzini wrote:
> 
> 
> On 23/09/2016 12:12, Peter Xu wrote:
> > On Fri, Sep 23, 2016 at 12:03:26PM +0200, Paolo Bonzini wrote:
> >>
> >>
> >> On 23/09/2016 12:02, Peter Xu wrote:
> >>> On Fri, Sep 23, 2016 at 11:27:09AM +0200, Paolo Bonzini wrote:
> >>>>> Since the whole IOMMU feature is new and somewhat experimental, I think
> >>>>> it's okay to just make EIM the default for >=2.8 machine types if KVM is
> >>>>> on (using DEFINE_PROP_ON_OFF_AUTO; auto means true if KVM is on and
> >>>>> false otherwise, and pc-2.7 would set eim=off). It means requiring
> >>>>> kernel 4.8 by default, but I don't think it's a big deal.
> >>> I think the problem is, even we have KVM support for x2apic, we are
> >>> still losing QEMU part. And guests with cluster x2apic and >8 vcpus
> >>> will not working properly on device interrupts, which can be very
> >>> confusing to people (it can boot, but some devices just don't work
> >>> properly, and they won't see useful information in guest dmesg).
> >>
> >> Yes, that's why I suggested EIM=on by default.
> > 
> > I am confused. :(
> > 
> > Why not we just keep people from that wrong configuration by default,
> > until we have x2apic in QEMU?
> 
> Do you mean Igor's patches?  I expect that they will go in pretty much
> at the same time as Radim's.

Ah! Yes we have x2apic all here... So I totally agree we should set it
on as default.

(My mistake of not noticing the truth)

Thanks,

-- peterx