x86: Dynamically allocate percpu data area when a CPU comes online.

At the same time, the data area starts life zeroed.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

1 files changed, 69 insertions, 0 deletions

diff --git a/xen/arch/x86/percpu.c b/xen/arch/x86/percpu.c
new file mode 100644
index 0000000000..ea82647b42
--- /dev/null
+++ b/xen/arch/x86/percpu.c
@@ -0,0 +1,69 @@
+#include <xen/config.h>
+#include <xen/percpu.h>
+#include <xen/cpu.h>
+#include <xen/init.h>
+#include <xen/mm.h>
+
+unsigned long __per_cpu_offset[NR_CPUS];
+#define INVALID_PERCPU_AREA (-(long)__per_cpu_start)
+#define PERCPU_ORDER (get_order_from_bytes(__per_cpu_data_end-__per_cpu_start))
+
+void __init percpu_init_areas(void)
+{
+    unsigned int cpu;
+    for ( cpu = 1; cpu < NR_CPUS; cpu++ )
+        __per_cpu_offset[cpu] = INVALID_PERCPU_AREA;
+}
+
+static int init_percpu_area(unsigned int cpu)
+{
+    char *p;
+    if ( __per_cpu_offset[cpu] != INVALID_PERCPU_AREA )
+        return 0;
+    if ( (p = alloc_xenheap_pages(PERCPU_ORDER, 0)) == NULL )
+        return -ENOMEM;
+    memset(p, 0, __per_cpu_data_end - __per_cpu_start);
+    __per_cpu_offset[cpu] = p - __per_cpu_start;
+    return 0;
+}
+
+static void free_percpu_area(unsigned int cpu)
+{
+    char *p = __per_cpu_start + __per_cpu_offset[cpu];
+    free_xenheap_pages(p, PERCPU_ORDER);
+    __per_cpu_offset[cpu] = INVALID_PERCPU_AREA;
+}
+
+static int cpu_percpu_callback(
+    struct notifier_block *nfb, unsigned long action, void *hcpu)
+{
+    unsigned int cpu = (unsigned long)hcpu;
+    int rc = 0;
+
+    switch ( action )
+    {
+    case CPU_UP_PREPARE:
+        rc = init_percpu_area(cpu);
+        break;
+    case CPU_UP_CANCELED:
+    case CPU_DEAD:
+        free_percpu_area(cpu);
+        break;
+    default:
+        break;
+    }
+
+    return !rc ? NOTIFY_DONE : notifier_from_errno(rc);
+}
+
+static struct notifier_block cpu_percpu_nfb = {
+    .notifier_call = cpu_percpu_callback,
+    .priority = 100 /* highest priority */
+};
+
+static int __init percpu_presmp_init(void)
+{
+    register_cpu_notifier(&cpu_percpu_nfb);
+    return 0;
+}
+presmp_initcall(percpu_presmp_init);