This is a note to let you know that I've just added the patch titled
xen/smp: Fix crash when booting with ACPI hotplug CPUs.
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xen-smp-fix-crash-when-booting-with-acpi-hotplug-cpus.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From cf405ae612b0f7e2358db7ff594c0e94846137aa Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <[email protected]>
Date: Thu, 26 Apr 2012 13:50:03 -0400
Subject: xen/smp: Fix crash when booting with ACPI hotplug CPUs.
From: Konrad Rzeszutek Wilk <[email protected]>
commit cf405ae612b0f7e2358db7ff594c0e94846137aa upstream.
When we boot on a machine that can hotplug CPUs and we
are using 'dom0_max_vcpus=X' on the Xen hypervisor line
to clip the amount of CPUs available to the initial domain,
we get this:
(XEN) Command line: com1=115200,8n1 dom0_mem=8G noreboot dom0_max_vcpus=8
sync_console mce_verbosity=verbose console=com1,vga loglvl=all guest_loglvl=all
.. snip..
DMI: Intel Corporation S2600CP/S2600CP, BIOS
SE5C600.86B.99.99.x032.072520111118 07/25/2011
.. snip.
SMP: Allowing 64 CPUs, 32 hotplug CPUs
installing Xen timer for CPU 7
cpu 7 spinlock event irq 361
NMI watchdog: disabled (cpu7): hardware events not enabled
Brought up 8 CPUs
.. snip..
[acpi processor finds the CPUs are not initialized and starts calling
arch_register_cpu, which creates /sys/devices/system/cpu/cpu8/online]
CPU 8 got hotplugged
CPU 9 got hotplugged
CPU 10 got hotplugged
.. snip..
initcall 1_acpi_battery_init_async+0x0/0x1b returned 0 after 406 usecs
calling erst_init+0x0/0x2bb @ 1
[and the scheduler sticks newly started tasks on the new CPUs, but
said CPUs cannot be initialized b/c the hypervisor has limited the
amount of vCPUS to 8 - as per the dom0_max_vcpus=8 flag.
The spinlock tries to kick the other CPU, but the structure for that
is not initialized and we crash.]
BUG: unable to handle kernel paging request at fffffffffffffed8
IP: [<ffffffff81035289>] xen_spin_lock+0x29/0x60
PGD 180d067 PUD 180e067 PMD 0
Oops: 0002 [#1] SMP
CPU 7
Modules linked in:
Pid: 1, comm: swapper/0 Not tainted 3.4.0-rc2upstream-00001-gf5154e8 #1 Intel
Corporation S2600CP/S2600CP
RIP: e030:[<ffffffff81035289>] [<ffffffff81035289>] xen_spin_lock+0x29/0x60
RSP: e02b:ffff8801fb9b3a70 EFLAGS: 00010282
With this patch, we cap the amount of vCPUS that the initial domain
can run, to exactly what dom0_max_vcpus=X has specified.
In the future, if there is a hypercall that will allow a running
domain to expand past its initial set of vCPUS, this patch should
be re-evaluated.
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/x86/xen/smp.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -172,6 +172,7 @@ static void __init xen_fill_possible_map
static void __init xen_filter_cpu_maps(void)
{
int i, rc;
+ unsigned int subtract = 0;
if (!xen_initial_domain())
return;
@@ -186,8 +187,22 @@ static void __init xen_filter_cpu_maps(v
} else {
set_cpu_possible(i, false);
set_cpu_present(i, false);
+ subtract++;
}
}
+#ifdef CONFIG_HOTPLUG_CPU
+ /* This is akin to using 'nr_cpus' on the Linux command line.
+ * Which is OK as when we use 'dom0_max_vcpus=X' we can only
+ * have up to X, while nr_cpu_ids is greater than X. This
+ * normally is not a problem, except when CPU hotplugging
+ * is involved and then there might be more than X CPUs
+ * in the guest - which will not work as there is no
+ * hypercall to expand the max number of VCPUs an already
+ * running guest has. So cap it up to X. */
+ if (subtract)
+ nr_cpu_ids = nr_cpu_ids - subtract;
+#endif
+
}
static void __init xen_smp_prepare_boot_cpu(void)
Patches currently in stable-queue which might be from [email protected] are
queue-3.0/xen-correctly-check-for-pending-events-when-restoring-irq-flags.patch
queue-3.0/xen-smp-fix-crash-when-booting-with-acpi-hotplug-cpus.patch
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