[PATCH] x86: fix PDA variables to work during boot

The current PDA code, which went in in post 2.6.19 has a flaw in that it
doesn't correctly cycle the GDT and %GS segment through the boot PDA,
the CPU PDA and finally the per-cpu PDA.

The bug generally doesn't show up if the boot CPU id is zero, but
everything falls apart for a non zero boot CPU id.  The basically kills
voyager which is perfectly capable of doing non zero CPU id boots, so
voyager currently won't boot without this.

The fix is to be careful and actually do the GDT setups correctly.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/i386/kernel/cpu/common.c

@@ -710,18 +710,22 @@ __cpuinit int init_gdt(int cpu, struct task_struct *idle)
 	return 1;
 }
 
-/* Common CPU init for both boot and secondary CPUs */
-static void __cpuinit _cpu_init(int cpu, struct task_struct *curr)
+void __cpuinit cpu_set_gdt(int cpu)
 {
-	struct tss_struct * t = &per_cpu(init_tss, cpu);
-	struct thread_struct *thread = &curr->thread;
 	struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu);
 
 	/* Reinit these anyway, even if they've already been done (on
 	   the boot CPU, this will transition from the boot gdt+pda to
 	   the real ones). */
 	load_gdt(cpu_gdt_descr);
 	set_kernel_gs();
+}
+
+/* Common CPU init for both boot and secondary CPUs */
+static void __cpuinit _cpu_init(int cpu, struct task_struct *curr)
+{
+	struct tss_struct * t = &per_cpu(init_tss, cpu);
+	struct thread_struct *thread = &curr->thread;
 
 	if (cpu_test_and_set(cpu, cpu_initialized)) {
 		printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);
@@ -807,6 +811,7 @@ void __cpuinit cpu_init(void)
 			local_irq_enable();
 	}
 
+	cpu_set_gdt(cpu);
 	_cpu_init(cpu, curr);
 }
 

arch/i386/kernel/smpboot.c

@@ -595,6 +595,12 @@ static void __cpuinit start_secondary(void *unused)
  */
 void __devinit initialize_secondary(void)
 {
+	/*
+	 * switch to the per CPU GDT we already set up
+	 * in do_boot_cpu()
+	 */
+	cpu_set_gdt(current_thread_info()->cpu);
+
 	/*
 	 * We don't actually need to load the full TSS,
 	 * basically just the stack pointer and the eip.
@@ -972,9 +978,6 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu)
 	/* Stack for startup_32 can be just as for start_secondary onwards */
 	stack_start.esp = (void *) idle->thread.esp;
 
-	start_pda = cpu_pda(cpu);
-	cpu_gdt_descr = per_cpu(cpu_gdt_descr, cpu);
-
 	irq_ctx_init(cpu);
 
 	x86_cpu_to_apicid[cpu] = apicid;

arch/i386/mach-voyager/voyager_smp.c

@@ -772,6 +772,12 @@ initialize_secondary(void)
 	set_current(hard_get_current());
 #endif
 
+	/*
+	 * switch to the per CPU GDT we already set up
+	 * in do_boot_cpu()
+	 */
+	cpu_set_gdt(current_thread_info()->cpu);
+
 	/*
 	 * We don't actually need to load the full TSS,
 	 * basically just the stack pointer and the eip.

include/asm-i386/processor.h

@@ -743,6 +743,7 @@ extern void enable_sep_cpu(void);
 extern int sysenter_setup(void);
 
 extern int init_gdt(int cpu, struct task_struct *idle);
+extern void cpu_set_gdt(int);
 extern void secondary_cpu_init(void);
 
 #endif /* __ASM_I386_PROCESSOR_H */