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

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Date:	Thu, 21 Aug 2008 15:16:52 +0200
From:	Robert Richter <robert.richter@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jan Beulich <jbeulich@...ell.com>, linux-kernel@...r.kernel.org
Subject: Re: patch "x86: MOVE PCI IO ECS code to x86/pci" breaks CPU hotplug

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.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center
email: robert.richter@....com

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