linux-kernel - [PATCH v4 48/57] x86: remove 64-byte gap at end of irq stack

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Message-Id: <55e077f77d86fbd543cb808fc18b0a53415cc1e2.1471525031.git.jpoimboe@redhat.com>
Date:	Thu, 18 Aug 2016 08:06:28 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Brian Gerst <brgerst@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Byungchul Park <byungchul.park@....com>,
	Nilay Vaish <nilayvaish@...il.com>
Subject: [PATCH v4 48/57] x86: remove 64-byte gap at end of irq stack

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@...hat.com>
---
 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 8be240f..33f3142 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