[POWERPC] Add IRQSTACKS support on ppc32

This makes it possible to use separate stacks for hard and soft IRQs
on 32-bit powerpc as well as on 64-bit.  The code for 32-bit is just
the 32-bit analog of the 64-bit code.

* Added allocation and initialization of the irq stacks.  We limit the
  stacks to be in lowmem for ppc32.
* Implemented ppc32 versions of call_do_softirq() and call_handle_irq()
  to switch the stack pointers
* Reworked how we do stack overflow detection.  We now keep around the
  limit of the stack in the thread_struct and compare against the limit
  to see if we've overflowed.  We can now use this on ppc64 if desired.

[ paulus@samba.org: Fixed bug on 6xx where we need to reload r9 with the
  thread_info pointer. ]

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

7 files changed, 60 insertions, 5 deletions

diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 807a2dce6263..a7d24e692bab 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -118,7 +118,6 @@ config XMON_DISASSEMBLY
 
 config IRQSTACKS
         bool "Use separate kernel stacks when processing interrupts"
-        depends on PPC64
         help
           If you say Y here the kernel will use separate kernel stacks
           for handling hard and soft interrupts.  This can help avoid
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 62134845af08..af1d2c894ee1 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -67,6 +67,7 @@ int main(void)
 #endif /* CONFIG_PPC64 */
 
         DEFINE(KSP, offsetof(struct thread_struct, ksp));
+        DEFINE(KSP_LIMIT, offsetof(struct thread_struct, ksp_limit));
         DEFINE(PT_REGS, offsetof(struct thread_struct, regs));
         DEFINE(THREAD_FPEXC_MODE, offsetof(struct thread_struct, fpexc_mode));
         DEFINE(THREAD_FPR0, offsetof(struct thread_struct, fpr[0]));
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 84c868633068..0c8614d9875c 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -137,11 +137,12 @@ transfer_to_handler:
 2:      /* if from kernel, check interrupted DOZE/NAP mode and
          * check for stack overflow
          */
-        lwz     r9,THREAD_INFO-THREAD(r12)
-        cmplw   r1,r9                   /* if r1 <= current->thread_info */
+        lwz     r9,KSP_LIMIT(r12)
+        cmplw   r1,r9                   /* if r1 <= ksp_limit */
         ble-    stack_ovf               /* then the kernel stack overflowed */
 5:
 #ifdef CONFIG_6xx
+        rlwinm  r9,r1,0,0,31-THREAD_SHIFT
         tophys(r9,r9)                   /* check local flags */
         lwz     r12,TI_LOCAL_FLAGS(r9)
         mtcrf   0x01,r12
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 425616f92d18..2f73f705d564 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -307,6 +307,7 @@ void do_IRQ(struct pt_regs *regs)
                 if (curtp != irqtp) {
                         struct irq_desc *desc = irq_desc + irq;
                         void *handler = desc->handle_irq;
+                        unsigned long saved_sp_limit = current->thread.ksp_limit;
                         if (handler == NULL)
                                 handler = &__do_IRQ;
                         irqtp->task = curtp->task;
@@ -319,7 +320,10 @@ void do_IRQ(struct pt_regs *regs)
                                 (irqtp->preempt_count & ~SOFTIRQ_MASK) |
                                 (curtp->preempt_count & SOFTIRQ_MASK);
 
+                        current->thread.ksp_limit = (unsigned long)irqtp +
+                                _ALIGN_UP(sizeof(struct thread_info), 16);
                         call_handle_irq(irq, desc, irqtp, handler);
+                        current->thread.ksp_limit = saved_sp_limit;
                         irqtp->task = NULL;
 
 
@@ -352,9 +356,7 @@ void __init init_IRQ(void)
 {
         if (ppc_md.init_IRQ)
                 ppc_md.init_IRQ();
-#ifdef CONFIG_PPC64
         irq_ctx_init();
-#endif
 }
 
 
@@ -383,11 +385,15 @@ void irq_ctx_init(void)
 static inline void do_softirq_onstack(void)
 {
         struct thread_info *curtp, *irqtp;
+        unsigned long saved_sp_limit = current->thread.ksp_limit;
 
         curtp = current_thread_info();
         irqtp = softirq_ctx[smp_processor_id()];
         irqtp->task = curtp->task;
+        current->thread.ksp_limit = (unsigned long)irqtp +
+                                    _ALIGN_UP(sizeof(struct thread_info), 16);
         call_do_softirq(irqtp);
+        current->thread.ksp_limit = saved_sp_limit;
         irqtp->task = NULL;
 }
 
diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
index 92ccc6fcc5b0..89aaaa6f3561 100644
--- a/arch/powerpc/kernel/misc_32.S
+++ b/arch/powerpc/kernel/misc_32.S
@@ -32,6 +32,31 @@
 
         .text
 
+#ifdef CONFIG_IRQSTACKS
+_GLOBAL(call_do_softirq)
+        mflr    r0
+        stw     r0,4(r1)
+        stwu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)
+        mr      r1,r3
+        bl      __do_softirq
+        lwz     r1,0(r1)
+        lwz     r0,4(r1)
+        mtlr    r0
+        blr
+
+_GLOBAL(call_handle_irq)
+        mflr    r0
+        stw     r0,4(r1)
+        mtctr   r6
+        stwu    r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r5)
+        mr      r1,r5
+        bctrl
+        lwz     r1,0(r1)
+        lwz     r0,4(r1)
+        mtlr    r0
+        blr
+#endif /* CONFIG_IRQSTACKS */
+
 /*
  * This returns the high 64 bits of the product of two 64-bit numbers.
  */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 6caad17ea72e..7de41c3948ec 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -589,6 +589,8 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
         kregs = (struct pt_regs *) sp;
         sp -= STACK_FRAME_OVERHEAD;
         p->thread.ksp = sp;
+        p->thread.ksp_limit = (unsigned long)task_stack_page(p) +
+                                _ALIGN_UP(sizeof(struct thread_info), 16);
 
 #ifdef CONFIG_PPC64
         if (cpu_has_feature(CPU_FTR_SLB)) {
diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
index 36f6779c88d4..5112a4aa801d 100644
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -16,6 +16,7 @@
 #include <linux/root_dev.h>
 #include <linux/cpu.h>
 #include <linux/console.h>
+#include <linux/lmb.h>
 
 #include <asm/io.h>
 #include <asm/prom.h>
@@ -229,6 +230,24 @@ int __init ppc_init(void)
 
 arch_initcall(ppc_init);
 
+#ifdef CONFIG_IRQSTACKS
+static void __init irqstack_early_init(void)
+{
+        unsigned int i;
+
+        /* interrupt stacks must be in lowmem, we get that for free on ppc32
+         * as the lmb is limited to lowmem by LMB_REAL_LIMIT */
+        for_each_possible_cpu(i) {
+                softirq_ctx[i] = (struct thread_info *)
+                        __va(lmb_alloc(THREAD_SIZE, THREAD_SIZE));
+                hardirq_ctx[i] = (struct thread_info *)
+                        __va(lmb_alloc(THREAD_SIZE, THREAD_SIZE));
+        }
+}
+#else
+#define irqstack_early_init()
+#endif
+
 /* Warning, IO base is not yet inited */
 void __init setup_arch(char **cmdline_p)
 {
@@ -286,6 +305,8 @@ void __init setup_arch(char **cmdline_p)
         init_mm.end_data = (unsigned long) _edata;
         init_mm.brk = klimit;
 
+        irqstack_early_init();
+
         /* set up the bootmem stuff with available memory */
         do_init_bootmem();
         if ( ppc_md.progress ) ppc_md.progress("setup_arch: bootmem", 0x3eab);