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

[Peter Xu]

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?

-- peterx