x86: change init_gdt to update the gdt via write_gdt, rather than a direct write.

By writing directly, a memory access violation can occur whilst
hotplugging a CPU if the entry was previously marked read-only.

Signed-off-by: Alex Nixon <alex.nixon@citrix.com>
Cc: Jeremy Fitzhardinge <Jeremy.Fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/smpcommon.c b/arch/x86/kernel/smpcommon.c
index 99941b3..397e309 100644 (file)
--- a/arch/x86/kernel/smpcommon.c
+++ b/arch/x86/kernel/smpcommon.c
@@ -8,18 +8,21 @@
 DEFINE_PER_CPU(unsigned long, this_cpu_off);
 EXPORT_PER_CPU_SYMBOL(this_cpu_off);
 
-/* Initialize the CPU's GDT.  This is either the boot CPU doing itself
-   (still using the master per-cpu area), or a CPU doing it for a
-   secondary which will soon come up. */
+/*
+ * Initialize the CPU's GDT.  This is either the boot CPU doing itself
+ * (still using the master per-cpu area), or a CPU doing it for a
+ * secondary which will soon come up.
+ */
 __cpuinit void init_gdt(int cpu)
 {
-       struct desc_struct *gdt = get_cpu_gdt_table(cpu);
+       struct desc_struct gdt;
 
-       pack_descriptor(&gdt[GDT_ENTRY_PERCPU],
-                       __per_cpu_offset[cpu], 0xFFFFF,
+       pack_descriptor(&gdt, __per_cpu_offset[cpu], 0xFFFFF,
                        0x2 | DESCTYPE_S, 0x8);
+       gdt.s = 1;
 
-       gdt[GDT_ENTRY_PERCPU].s = 1;
+       write_gdt_entry(get_cpu_gdt_table(cpu),
+                       GDT_ENTRY_PERCPU, &gdt, DESCTYPE_S);
 
        per_cpu(this_cpu_off, cpu) = __per_cpu_offset[cpu];
        per_cpu(cpu_number, cpu) = cpu;