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authorPaul Mackerras <paulus@samba.org>2012-10-15 01:15:41 +0000
committerAlexander Graf <agraf@suse.de>2012-10-30 10:54:53 +0100
commit512691d4907d7cf4b8d05c6f8572d1fa60ccec20 (patch)
tree8cb0fb7f8cdc1b0283ef7cba585775f47b974ebc /arch/powerpc/kernel
parentc99ec973a63e2249020d6d93a46d7572432da6a2 (diff)
downloadop-kernel-dev-512691d4907d7cf4b8d05c6f8572d1fa60ccec20.zip
op-kernel-dev-512691d4907d7cf4b8d05c6f8572d1fa60ccec20.tar.gz
KVM: PPC: Book3S HV: Allow KVM guests to stop secondary threads coming online
When a Book3S HV KVM guest is running, we need the host to be in single-thread mode, that is, all of the cores (or at least all of the cores where the KVM guest could run) to be running only one active hardware thread. This is because of the hardware restriction in POWER processors that all of the hardware threads in the core must be in the same logical partition. Complying with this restriction is much easier if, from the host kernel's point of view, only one hardware thread is active. This adds two hooks in the SMP hotplug code to allow the KVM code to make sure that secondary threads (i.e. hardware threads other than thread 0) cannot come online while any KVM guest exists. The KVM code still has to check that any core where it runs a guest has the secondary threads offline, but having done that check it can now be sure that they will not come online while the guest is running. Signed-off-by: Paul Mackerras <paulus@samba.org> Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Alexander Graf <agraf@suse.de>
Diffstat (limited to 'arch/powerpc/kernel')
-rw-r--r--arch/powerpc/kernel/smp.c46
1 files changed, 46 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 8d4214a..c4f420c 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -417,6 +417,45 @@ int generic_check_cpu_restart(unsigned int cpu)
{
return per_cpu(cpu_state, cpu) == CPU_UP_PREPARE;
}
+
+static atomic_t secondary_inhibit_count;
+
+/*
+ * Don't allow secondary CPU threads to come online
+ */
+void inhibit_secondary_onlining(void)
+{
+ /*
+ * This makes secondary_inhibit_count stable during cpu
+ * online/offline operations.
+ */
+ get_online_cpus();
+
+ atomic_inc(&secondary_inhibit_count);
+ put_online_cpus();
+}
+EXPORT_SYMBOL_GPL(inhibit_secondary_onlining);
+
+/*
+ * Allow secondary CPU threads to come online again
+ */
+void uninhibit_secondary_onlining(void)
+{
+ get_online_cpus();
+ atomic_dec(&secondary_inhibit_count);
+ put_online_cpus();
+}
+EXPORT_SYMBOL_GPL(uninhibit_secondary_onlining);
+
+static int secondaries_inhibited(void)
+{
+ return atomic_read(&secondary_inhibit_count);
+}
+
+#else /* HOTPLUG_CPU */
+
+#define secondaries_inhibited() 0
+
#endif
static void cpu_idle_thread_init(unsigned int cpu, struct task_struct *idle)
@@ -435,6 +474,13 @@ int __cpuinit __cpu_up(unsigned int cpu, struct task_struct *tidle)
{
int rc, c;
+ /*
+ * Don't allow secondary threads to come online if inhibited
+ */
+ if (threads_per_core > 1 && secondaries_inhibited() &&
+ cpu % threads_per_core != 0)
+ return -EBUSY;
+
if (smp_ops == NULL ||
(smp_ops->cpu_bootable && !smp_ops->cpu_bootable(cpu)))
return -EINVAL;
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