[PATCH v4 1/2] powerpc/irq: bring back ksp_limit management in C functions.

[Christophe Leroy <christophe.leroy@c-s.fr>]

Commit cbc9565ee826 ("powerpc: Remove ksp_limit on ppc64") moved
PPC32 ksp_limit handling in assembly functions call_do_softirq()
and call_do_irq() as they are different for PPC32 and PPC64.

In preparation of replacing these functions by inline assembly,
partialy revert that commit to bring back ksp_limit assignment
in the callers.

To get and set ksp_limit without a forest of #ifdefs CONFIG_PPC32,
use helpers that will void on PPC64.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

---
v2: added forward declaration of struct task_struct to avoid build failure.
v3: included linux/sched.h, forward declaration is not enough.
v4: no change
---
 arch/powerpc/include/asm/irq.h | 22 ++++++++++++++++++++++
 arch/powerpc/kernel/irq.c      | 14 +++++++++++++-
 arch/powerpc/kernel/misc_32.S  | 14 --------------
 3 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/include/asm/irq.h b/arch/powerpc/include/asm/irq.h
index 814dfab7e392..0c6469983c66 100644
--- a/arch/powerpc/include/asm/irq.h
+++ b/arch/powerpc/include/asm/irq.h
@@ -10,6 +10,7 @@
 #include <linux/threads.h>
 #include <linux/list.h>
 #include <linux/radix-tree.h>
+#include <linux/sched.h>
 
 #include <asm/types.h>
 #include <linux/atomic.h>
@@ -64,5 +65,26 @@ extern void __do_irq(struct pt_regs *regs);
 
 int irq_choose_cpu(const struct cpumask *mask);
 
+#ifdef CONFIG_PPC32
+static inline unsigned long get_ksp_limit(struct task_struct *tsk)
+{
+	return tsk->thread.ksp_limit;
+}
+
+static inline void set_ksp_limit(struct task_struct *tsk, unsigned long limit)
+{
+	tsk->thread.ksp_limit = limit;
+}
+#else
+static inline unsigned long get_ksp_limit(struct task_struct *tsk)
+{
+	return 0;
+}
+
+static inline void set_ksp_limit(struct task_struct *tsk, unsigned long limit)
+{
+}
+#endif
+
 #endif /* _ASM_IRQ_H */
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 5645bc9cbc09..04204be49577 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -646,6 +646,7 @@ void do_IRQ(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);
 	void *cursp, *irqsp, *sirqsp;
+	unsigned long saved_ksp_limit = get_ksp_limit(current);
 
 	/* Switch to the irq stack to handle this */
 	cursp = (void *)(current_stack_pointer() & ~(THREAD_SIZE - 1));
@@ -658,9 +659,15 @@ void do_IRQ(struct pt_regs *regs)
 		set_irq_regs(old_regs);
 		return;
 	}
+	/* Adjust the stack limit */
+	set_ksp_limit(current, (unsigned long)irqsp);
+
 	/* Switch stack and call */
 	call_do_irq(regs, irqsp);
 
+	/* Restore stack limit */
+	set_ksp_limit(current, saved_ksp_limit);
+
 	set_irq_regs(old_regs);
 }
 
@@ -681,7 +688,12 @@ void *hardirq_ctx[NR_CPUS] __read_mostly;
 
 void do_softirq_own_stack(void)
 {
-	call_do_softirq(softirq_ctx[smp_processor_id()]);
+	void *irqsp = softirq_ctx[smp_processor_id()];
+	unsigned long saved_ksp_limit = get_ksp_limit(current);
+
+	set_ksp_limit(current, (unsigned long)irqsp);
+	call_do_softirq(irqsp);
+	set_ksp_limit(current, saved_ksp_limit);
 }
 
 irq_hw_number_t virq_to_hw(unsigned int virq)
diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
index 82df4b09e79f..a5422f7782b3 100644
--- a/arch/powerpc/kernel/misc_32.S
+++ b/arch/powerpc/kernel/misc_32.S
@@ -33,23 +33,14 @@
 
 	.text
 
-/*
- * We store the saved ksp_limit in the unused part
- * of the STACK_FRAME_OVERHEAD
- */
 _GLOBAL(call_do_softirq)
 	mflr	r0
 	stw	r0,4(r1)
-	lwz	r10,THREAD+KSP_LIMIT(r2)
-	stw	r3, THREAD+KSP_LIMIT(r2)
 	stwu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)
 	mr	r1,r3
-	stw	r10,8(r1)
 	bl	__do_softirq
-	lwz	r10,8(r1)
 	lwz	r1,0(r1)
 	lwz	r0,4(r1)
-	stw	r10,THREAD+KSP_LIMIT(r2)
 	mtlr	r0
 	blr
 
@@ -59,16 +50,11 @@ _GLOBAL(call_do_softirq)
 _GLOBAL(call_do_irq)
 	mflr	r0
 	stw	r0,4(r1)
-	lwz	r10,THREAD+KSP_LIMIT(r2)
-	stw	r4, THREAD+KSP_LIMIT(r2)
 	stwu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)
 	mr	r1,r4
-	stw	r10,8(r1)
 	bl	__do_irq
-	lwz	r10,8(r1)
 	lwz	r1,0(r1)
 	lwz	r0,4(r1)
-	stw	r10,THREAD+KSP_LIMIT(r2)
 	mtlr	r0
 	blr
 
-- 
2.13.3