linux-kernel - Re: patch "x86: MOVE PCI IO ECS code to x86/pci" breaks CPU hotplug

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Date:	Fri, 22 Aug 2008 08:05:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Richter <robert.richter@....com>
Cc:	Jan Beulich <jbeulich@...ell.com>, linux-kernel@...r.kernel.org,
	Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: patch "x86: MOVE PCI IO ECS code to x86/pci" breaks CPU hotplug


* Robert Richter <robert.richter@....com> wrote:

> On 21.08.08 15:02:59, Ingo Molnar wrote:
> > 
> > * Jan Beulich <jbeulich@...ell.com> wrote:
> > 
> > > Converting __cpuinit functions called out of init_amd() (and similar 
> > > others) to __init (and making them subject of xxx_initcall() handling 
> > > isn't valid, as they would no longer be called for hot plugged CPUs.
> > > 
> > > Further, since it's likely that in virtualized environments the MSR 
> > > write would at best be ignored, I'd also recommend using the 
> > > fault-safe accessors here *and* check that the bit actually got set 
> > > before setting PCI_HAS_IO_ECS (one would obviously have to BUG() when 
> > > hot-plugged CPUs fail to set the bit when those available at boot 
> > > successfully did so).
> > 
> > hm, which patch is this exactly, and in what tree? It's not upstream nor 
> > in -tip.
> 
> Probably this in the mainline kernel is meant:
> 
> commit 3a27dd1ce5de08e21e0266ddf00e6f1f843bfe8b
> Author: Robert Richter <robert.richter@....com>
> Date:   Thu Jun 12 20:19:23 2008 +0200
> 
>     x86: Move PCI IO ECS code to x86/pci
>     
>     "Form follows function". Code is now where it belongs to.
>     
>     Signed-off-by: Robert Richter <robert.richter@....com>
>     Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> The problem is code like this:
> 
> +static int __init enable_pci_io_ecs(void)
> +{
> +       /* assume all cpus from fam10h have IO ECS */
> +        if (boot_cpu_data.x86 < 0x10)
> +               return 0;
> +       on_each_cpu(enable_pci_io_ecs_per_cpu, NULL, 1, 1);
> +       pci_probe |= PCI_HAS_IO_ECS;
> +       return 0;
> +}
> 
> It is only called during the setup and if the cpu is enabled. I intend 
> to rewrite the cpu setup code using cpu notifiers.

ok. Unfortunately the revert looks quite non-trivial for v2.6.27. Could 
we have some _really_ minimal fix for v2.6.27?

	Ingo
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