[PATCH 1/3] arm: introduce self pointer in thread info

[Maninder Singh]

self pointer to thread info is added in thread info.
It is base change required for IRQ stack on ARM.

both stacks will have pointer to thread_info at bottom.

Co-developed-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>
---
 arch/arm/Kconfig                   | 10 ++++++++++
 arch/arm/include/asm/assembler.h   |  3 +++
 arch/arm/include/asm/thread_info.h | 27 +++++++++++++++++++++++++++
 include/linux/thread_info.h        |  4 ++++
 kernel/fork.c                      |  1 +
 5 files changed, 45 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index fe2f17eb2..434442f 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1667,6 +1667,16 @@ config STACKPROTECTOR_PER_TASK
 	  Enable this option to switch to a different method that uses a
 	  different canary value for each task.
 
+config IRQ_STACK
+	bool "use separate stacks for Interrupts"
+	default n
+	depends on FRAME_POINTER && !CC_IS_CLANG
+	help
+	  Select this option to use separate stacks for Interrupt handling code.
+	  It will add latency in fetching thread info of one more derefer operation
+	  and add latency in Interrupt serve at time as for each Interrupt, thread_info
+	  pointer needs to be stored at bottom of interrupt stack.
+
 endmenu
 
 menu "Boot options"
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index fce52eed..8512bdc 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -207,6 +207,9 @@
  THUMB(	mov	\rd, sp			)
  THUMB(	lsr	\rd, \rd, #THREAD_SIZE_ORDER + PAGE_SHIFT	)
 	mov	\rd, \rd, lsl #THREAD_SIZE_ORDER + PAGE_SHIFT
+#ifdef CONFIG_IRQ_STACK
+	ldr	\rd, [\rd]
+#endif
 	.endm
 
 /*
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 536b6b9..a4d5f76 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -44,6 +44,9 @@ struct cpu_context_save {
  * __switch_to() assumes cpu_context follows immediately after cpu_domain.
  */
 struct thread_info {
+#ifdef CONFIG_IRQ_STACK
+	void			*tinfo_ptr;	/* pointer to self thread_info */
+#endif
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
 	mm_segment_t		addr_limit;	/* address limit */
@@ -67,14 +70,33 @@ struct thread_info {
 #endif
 };
 
+
+#ifdef CONFIG_IRQ_STACK
+#define INIT_THREAD_SELF_PTR				\
+	.tinfo_ptr	= &init_thread_union.thread_info,
+#else
+#define INIT_THREAD_SELF_PTR
+#endif
+
 #define INIT_THREAD_INFO(tsk)						\
 {									\
+	INIT_THREAD_SELF_PTR						\
 	.task		= &tsk,						\
 	.flags		= 0,						\
 	.preempt_count	= INIT_PREEMPT_COUNT,				\
 	.addr_limit	= KERNEL_DS,					\
 }
 
+
+#ifdef CONFIG_IRQ_STACK
+#define TASK_THREAD_SELF_POINTER(tsk)				\
+{								\
+	struct thread_info *ti = task_thread_info(tsk);		\
+								\
+	ti->tinfo_ptr = ti;					\
+}
+#endif
+
 /*
  * how to get the thread information struct from C
  */
@@ -82,8 +104,13 @@ struct thread_info {
 
 static inline struct thread_info *current_thread_info(void)
 {
+#ifdef CONFIG_IRQ_STACK
+	return (struct thread_info *)
+		(*((unsigned long *)(current_stack_pointer & ~(THREAD_SIZE - 1))));
+#else
 	return (struct thread_info *)
 		(current_stack_pointer & ~(THREAD_SIZE - 1));
+#endif
 }
 
 #define thread_saved_pc(tsk)	\
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index e93e249..ddf7b43 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -43,6 +43,10 @@ enum {
 #define THREAD_ALIGN	THREAD_SIZE
 #endif
 
+#ifndef TASK_THREAD_SELF_POINTER
+#define TASK_THREAD_SELF_POINTER(tsk)
+#endif
+
 #define THREADINFO_GFP		(GFP_KERNEL_ACCOUNT | __GFP_ZERO)
 
 /*
diff --git a/kernel/fork.c b/kernel/fork.c
index 7ef3eb3..d53f5eb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -901,6 +901,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 #endif
 
 	setup_thread_stack(tsk, orig);
+	TASK_THREAD_SELF_POINTER(tsk);
 	clear_user_return_notifier(tsk);
 	clear_tsk_need_resched(tsk);
 	set_task_stack_end_magic(tsk);
-- 
1.9.1