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>
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 98ea26a2..a0a2b5c 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -242,13 +242,10 @@
/* Set up %gs.
*
- * On SMP, %gs should point to the per-cpu area. For initial
- * boot, make %gs point to the init data section. For a
- * secondary CPU,initial_gs should be set to its pda address
- * before the CPU runs this code.
- *
- * On UP, initial_gs points to PER_CPU_VAR(__pda) and doesn't
- * change.
+ * The base of %gs always points to the bottom of the irqstack
+ * union. If the stack protector canary is enabled, it is
+ * located at %gs:40. Note that, on SMP, the boot cpu uses
+ * init data section till per cpu areas are set up.
*/
movl $MSR_GS_BASE,%ecx
movq initial_gs(%rip),%rax
@@ -281,7 +278,7 @@
#ifdef CONFIG_SMP
.quad __per_cpu_load
#else
- .quad PER_CPU_VAR(__pda)
+ .quad PER_CPU_VAR(irq_stack_union)
#endif
__FINITDATA