x86: move stack_canary into irq_stack

Impact: x86_64 percpu area layout change, irq_stack now at the beginning

Now that the PDA is empty except for the stack canary, it can be removed.
The irqstack is moved to the start of the per-cpu section.  If the stack
protector is enabled, the canary overlaps the bottom 48 bytes of the irqstack.

tj: * updated subject
    * dropped asm relocation of irq_stack_ptr
    * updated comments a bit
    * rebased on top of stack canary changes

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index f83a4d6160f..098934e72a1 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -881,12 +881,13 @@ __setup("clearcpuid=", setup_disablecpuid);
 #ifdef CONFIG_X86_64
 struct desc_ptr idt_descr = { 256 * 16 - 1, (unsigned long) idt_table };
 
-DEFINE_PER_CPU_PAGE_ALIGNED(char[IRQ_STACK_SIZE], irq_stack);
+DEFINE_PER_CPU_FIRST(union irq_stack_union,
+                     irq_stack_union) __aligned(PAGE_SIZE);
 #ifdef CONFIG_SMP
 DEFINE_PER_CPU(char *, irq_stack_ptr);  /* will be set during per cpu init */
 #else
 DEFINE_PER_CPU(char *, irq_stack_ptr) =
-        per_cpu_var(irq_stack) + IRQ_STACK_SIZE - 64;
+        per_cpu_var(irq_stack_union.irq_stack) + IRQ_STACK_SIZE - 64;
 #endif
 
 DEFINE_PER_CPU(unsigned long, kernel_stack) =
@@ -960,7 +961,7 @@ void __cpuinit cpu_init(void)
 
         loadsegment(fs, 0);
         loadsegment(gs, 0);
-        load_pda_offset(cpu);
+        load_gs_base(cpu);
 
 #ifdef CONFIG_NUMA
         if (cpu != 0 && percpu_read(node_number) == 0 &&