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

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Message-ID: <20120706113209.GB18059@amt.cnet>
Date:	Fri, 6 Jul 2012 08:32:09 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"Michael S. Tsirkin" <mst@...hat.com>, Avi Kivity <avi@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Rothwell <sfr@...b.auug.org.au>, x86@...nel.org,
	kvm@...r.kernel.org, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] apic: fix kvm build on UP without IOAPIC

On Fri, Jul 06, 2012 at 01:13:14PM +0200, Ingo Molnar wrote:
> 
> * H. Peter Anvin <hpa@...or.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@...hat.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

This tree (kvm.git next):

http://git.kernel.org/?p=virt/kvm/kvm.git;a=shortlog;h=refs/heads/next

Introduced by this commit:

http://git.kernel.org/?p=virt/kvm/kvm.git;a=commit;h=ab9cf4996bb989983e73da894b8dd0239aa2c3c2


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