Re: [PATCH] apic: fix kvm build on UP without IOAPIC

Marcelo Tosatti
2012-07-06T11:32:09Z

On Fri, Jul 06, 2012 at 01:13:14PM +0200, Ingo Molnar wrote:
>
> * H. Peter Anvin <hpa@zytor.com> wrote:
>
> > On 07/01/2012 08:05 AM, Michael S. Tsirkin wrote:
> > >On UP i386, when APIC is disabled
> > ># CONFIG_X86_UP_APIC is not set
> > ># CONFIG_PCI_IOAPIC is not set
> > >
> > >code looking at apicdrivers never has any effect but it
> > >still gets compiled in. In particular, this causes
> > >build failures with kvm, but it generally bloats the kernel
> > >unnecessarily.
> > >
> > >Fix by defining both __apicdrivers and __apicdrivers_end
> > >to be NULL when CONFIG_X86_LOCAL_APIC is unset: I verified
> > >that as the result any loop scanning __apicdrivers gets optimized out by
> > >the compiler.
> > >
> > >Warning: a .config with apic disabled doesn't seem to boot
> > >for me (even without this patch). Still verifying why,
> > >meanwhile this patch is compile-tested only.
> > >
> > >Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > >---
> > >
> > >Note: if this patch makes sense, can x86 maintainers
> > >please ACK applying it through the kvm tree, since that is
> > >where we see the issue that it addresses?
> > >Avi, Marcelo, maybe you can carry this in kvm/linux-next as a temporary
> > >measure so that linux-next builds?
> > >
> >
> > I'm not happy about that as a workflow, but since you guys have an
> > immediate problem I guess we can do that.
>
> I'm rather unhappy about this workflow - we've got quite a few
> apic bits in the x86 tree this cycle as well and need extra
> external interaction, not.
>
> Which KVM tree commit caused this, could someone please give a
> lkml link or quote it here? It's not referenced in the fix patch
> either.
>
> Thanks,
>
> Ingo