[Xen-devel] [PATCH v3 10/10] xen/arm: Enable errata for secondary CPU on hotplug after the boot

[Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>]

On boot, enabling errata workarounds will be triggered by the boot CPU
from start_xen(). On CPU hotplug (non-boot scenario) this would not be
done. This patch adds the code required to enable errata workarounds
for a CPU being hotplugged after the system boots. This is triggered
using a notifier. If the CPU fails to enable the errata Xen will panic.
This is done because it is assumed that the CPU which is hotplugged
after the system/Xen boots, was initially hotplugged during the
system/Xen boot. Therefore, enabling errata workarounds should never
fail.

Signed-off-by: Mirela Simonovic <mirela.simonovic@xxxxxxxxxx>

---
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/arm/cpuerrata.c         | 35 +++++++++++++++++++++++++++++++++++
 xen/arch/arm/cpufeature.c        | 23 +++++++++++++++++++++++
 xen/include/asm-arm/cpufeature.h |  1 +
 3 files changed, 59 insertions(+)

diff --git a/xen/arch/arm/cpuerrata.c b/xen/arch/arm/cpuerrata.c
index 1baa20654b..4040f781ec 100644
--- a/xen/arch/arm/cpuerrata.c
+++ b/xen/arch/arm/cpuerrata.c
@@ -5,6 +5,8 @@
 #include <xen/spinlock.h>
 #include <xen/vmap.h>
 #include <xen/warning.h>
+#include <xen/notifier.h>
+#include <xen/cpu.h>
 #include <asm/cpufeature.h>
 #include <asm/cpuerrata.h>
 #include <asm/psci.h>
@@ -349,6 +351,39 @@ void __init enable_errata_workarounds(void)
     enable_cpu_capabilities(arm_errata);
 }
 
+static int cpu_errata_callback(
+    struct notifier_block *nfb, unsigned long action, void *hcpu)
+{
+    switch ( action )
+    {
+    case CPU_STARTING:
+        enable_nonboot_cpu_caps(arm_errata);
+        break;
+    default:
+        break;
+    }
+
+    return NOTIFY_DONE;
+}
+
+static struct notifier_block cpu_errata_nfb = {
+    .notifier_call = cpu_errata_callback,
+};
+
+static int __init cpu_errata_notifier_init(void)
+{
+    register_cpu_notifier(&cpu_errata_nfb);
+    return 0;
+}
+/*
+ * Initialization has to be done at init rather than presmp_init phase because
+ * the callback should execute only after the secondary CPUs are initially
+ * booted (in hotplug scenarios when the system state is not boot). On boot,
+ * the enabling of errata workarounds will be triggered by the boot CPU from
+ * start_xen().
+ */
+__initcall(cpu_errata_notifier_init);
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
index 525b45e22f..dd30f0d29c 100644
--- a/xen/arch/arm/cpufeature.c
+++ b/xen/arch/arm/cpufeature.c
@@ -68,6 +68,29 @@ void __init enable_cpu_capabilities(const struct 
arm_cpu_capabilities *caps)
     }
 }
 
+/* Run through the enabled capabilities and enable() them on the calling CPU */
+void enable_nonboot_cpu_caps(const struct arm_cpu_capabilities *caps)
+{
+    ASSERT(system_state != SYS_STATE_boot);
+
+    for ( ; caps->matches; caps++ )
+    {
+        if ( !cpus_have_cap(caps->capability) )
+            continue;
+
+        if ( caps->enable )
+        {
+            /*
+             * Since the CPU has enabled errata workarounds on boot, it should
+             * never fail to enable them here.
+             */
+            if ( caps->enable((void *)caps) )
+                panic("CPU%u failed to enable capability %u\n",
+                      smp_processor_id(), caps->capability);
+        }
+    }
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
index e557a095af..b14e226401 100644
--- a/xen/include/asm-arm/cpufeature.h
+++ b/xen/include/asm-arm/cpufeature.h
@@ -88,6 +88,7 @@ void update_cpu_capabilities(const struct 
arm_cpu_capabilities *caps,
                              const char *info);
 
 void enable_cpu_capabilities(const struct arm_cpu_capabilities *caps);
+void enable_nonboot_cpu_caps(const struct arm_cpu_capabilities *caps);
 
 #endif /* __ASSEMBLY__ */
 
-- 
2.13.0


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