Re: [PATCH] Revert "intel_iommu: Fix irqchip / X2APIC configuration checks"

[Peter Xu]

On Mon, Sep 26, 2022 at 11:33:11AM +0200, Igor Mammedov wrote:
> On Fri, 23 Sep 2022 21:27:08 -0400
> Peter Xu <peterx@redhat.com> wrote:
> 
> > On Fri, Sep 23, 2022 at 06:03:44PM -0400, Peter Xu wrote:
> > > On Fri, Sep 23, 2022 at 10:41:59AM +0200, Igor Mammedov wrote:  
> > > > It's worth putting history excavation with explanation what is broken 
> > > > and why
> > > > compat stuff is being ignored in the patch.  
> > > 
> > > Makes sense, I'll amend the commit message and repost.  Thanks,  
> > 
> > There's actually one way to slightly remedy this single case, mostly for
> > any QEMU 7.1.0 user with -smp <=8 and the intel iommu (as 77250171bdc02 is
> > merged only in 7.1.0).
> > 
> > We can have one compact parameter x-eim-enable-kvm-x2apic, setting it "on"
> > by default, "off" for 7.1, and "on" for 7.0-.
> > 
> > I'm not very sure whether that'll worth it.  Any thoughts?
> 
> How it (enabling x2apic API) would affect kvm/guests running with 8 or less 
> CPUs
> and with intel iommu + remapping?

It's more from the guest ABI level, but indeed at least from what I see so
far <=8 CPUs are fine.

I'll keep the patch short, thanks.

-- 
Peter Xu