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-rw-r--r--arch/x86/xen/smp.c15
1 files changed, 15 insertions, 0 deletions
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 501d4e0244b..f2ce60a3c45 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -172,6 +172,7 @@ static void __init xen_fill_possible_map(void)
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(void)
} 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)