[PATCH v3 45/51] x86: remove 64-byte gap at end of irq stack

From: Josh Poimboeuf
Date: Fri Aug 12 2016 - 10:34:12 EST


There has been a 64-byte gap at the end of the irq stack for at least 12
years. It predates git history, and I can't find any good reason for
it. Remove it. What's the worst that could happen?

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
arch/x86/include/asm/page_64_types.h | 3 ---
arch/x86/kernel/cpu/common.c | 2 +-
arch/x86/kernel/dumpstack_64.c | 4 ++--
arch/x86/kernel/setup_percpu.c | 2 +-
4 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index 6256baf..3c0be3b 100644
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -24,9 +24,6 @@
#define IRQ_STACK_ORDER (2 + KASAN_STACK_ORDER)
#define IRQ_STACK_SIZE (PAGE_SIZE << IRQ_STACK_ORDER)

-/* FIXME: why? */
-#define IRQ_USABLE_STACK_SIZE (IRQ_STACK_SIZE - 64)
-
#define DOUBLEFAULT_STACK 1
#define NMI_STACK 2
#define DEBUG_STACK 3
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 55684b1..ce7a4c1 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1286,7 +1286,7 @@ DEFINE_PER_CPU(struct task_struct *, current_task) ____cacheline_aligned =
EXPORT_PER_CPU_SYMBOL(current_task);

DEFINE_PER_CPU(char *, irq_stack_ptr) =
- init_per_cpu_var(irq_stack_union.irq_stack) + IRQ_USABLE_STACK_SIZE;
+ init_per_cpu_var(irq_stack_union.irq_stack) + IRQ_STACK_SIZE;

DEFINE_PER_CPU(unsigned int, irq_count) __visible = -1;

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 9f7a9f9..001a75d 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -78,7 +78,7 @@ static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
static bool in_irq_stack(unsigned long *stack, struct stack_info *info)
{
unsigned long *end = (unsigned long *)this_cpu_read(irq_stack_ptr);
- unsigned long *begin = end - (IRQ_USABLE_STACK_SIZE / sizeof(long));
+ unsigned long *begin = end - (IRQ_STACK_SIZE / sizeof(long));

if (stack < begin || stack >= end)
return false;
@@ -145,7 +145,7 @@ void show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
int i;

irq_stack_end = (unsigned long *)this_cpu_read(irq_stack_ptr);
- irq_stack = irq_stack_end - (IRQ_USABLE_STACK_SIZE / sizeof(long));
+ irq_stack = irq_stack_end - (IRQ_STACK_SIZE / sizeof(long));

sp = sp ? : get_stack_pointer(task, regs);

diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index a2a0eae..2bbd27f 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -246,7 +246,7 @@ void __init setup_per_cpu_areas(void)
#ifdef CONFIG_X86_64
per_cpu(irq_stack_ptr, cpu) =
per_cpu(irq_stack_union.irq_stack, cpu) +
- IRQ_USABLE_STACK_SIZE;
+ IRQ_STACK_SIZE;
#endif
#ifdef CONFIG_NUMA
per_cpu(x86_cpu_to_node_map, cpu) =
--
2.7.4