powerpc: Add irqtrace support for 32-bit powerpc

Based on initial work from: Dale Farnsworth <dale@farnsworth.org>

Add the low level irq tracing hooks for 32-bit powerpc needed
to enable full lockdep functionality.

The approach taken to deal with the code in entry_32.S is that
we don't trace all the transitions of MSR:EE when we just turn
it off to peek at TI_FLAGS without races. Only when we are
calling into C code or returning from exceptions with a state
that have changed from what lockdep thinks.

There's a little bugger though: If we take an exception that
keeps interrupts enabled (such as an alignment exception) while
interrupts are enabled, we will call trace_hardirqs_on() on the
way back spurriously. Not a big deal, but to get rid of it would
require remembering in pt_regs that the exception was one of the
type that kept interrupts enabled which we don't know at this
stage. (Well, we could test all cases for regs->trap but that
sucks too much).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Tested-by: Kumar Gala <galak@kernel.crashing.org>

4 files changed, 135 insertions, 15 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index bf6cedfa05db..d00131ca0835 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -62,7 +62,6 @@ config HAVE_LATENCYTOP_SUPPORT
 
 config TRACE_IRQFLAGS_SUPPORT
         bool
-        depends on PPC64
         default y
 
 config LOCKDEP_SUPPORT
diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index 867ab8ed69b3..8b505eaaa38a 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h
@@ -68,13 +68,13 @@ static inline int irqs_disabled_flags(unsigned long flags)
 
 #if defined(CONFIG_BOOKE)
 #define SET_MSR_EE(x)   mtmsr(x)
-#define local_irq_restore(flags)        __asm__ __volatile__("wrtee %0" : : "r" (flags) : "memory")
+#define raw_local_irq_restore(flags)    __asm__ __volatile__("wrtee %0" : : "r" (flags) : "memory")
 #else
 #define SET_MSR_EE(x)   mtmsr(x)
-#define local_irq_restore(flags)        mtmsr(flags)
+#define raw_local_irq_restore(flags)    mtmsr(flags)
 #endif
 
-static inline void local_irq_disable(void)
+static inline void raw_local_irq_disable(void)
 {
 #ifdef CONFIG_BOOKE
         __asm__ __volatile__("wrteei 0": : :"memory");
@@ -86,7 +86,7 @@ static inline void local_irq_disable(void)
 #endif
 }
 
-static inline void local_irq_enable(void)
+static inline void raw_local_irq_enable(void)
 {
 #ifdef CONFIG_BOOKE
         __asm__ __volatile__("wrteei 1": : :"memory");
@@ -98,7 +98,7 @@ static inline void local_irq_enable(void)
 #endif
 }
 
-static inline void local_irq_save_ptr(unsigned long *flags)
+static inline void raw_local_irq_save_ptr(unsigned long *flags)
 {
         unsigned long msr;
         msr = mfmsr();
@@ -110,12 +110,12 @@ static inline void local_irq_save_ptr(unsigned long *flags)
 #endif
 }
 
-#define local_save_flags(flags) ((flags) = mfmsr())
-#define local_irq_save(flags)   local_irq_save_ptr(&flags)
-#define irqs_disabled()         ((mfmsr() & MSR_EE) == 0)
+#define raw_local_save_flags(flags)     ((flags) = mfmsr())
+#define raw_local_irq_save(flags)       raw_local_irq_save_ptr(&flags)
+#define raw_irqs_disabled()             ((mfmsr() & MSR_EE) == 0)
+#define raw_irqs_disabled_flags(flags)  (((flags) & MSR_EE) == 0)
 
-#define hard_irq_enable()       local_irq_enable()
-#define hard_irq_disable()      local_irq_disable()
+#define hard_irq_disable()              raw_local_irq_disable()
 
 static inline int irqs_disabled_flags(unsigned long flags)
 {
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 4dd38f129153..3cadba60a4b6 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -191,11 +191,49 @@ transfer_to_handler_cont:
         mflr    r9
         lwz     r11,0(r9)               /* virtual address of handler */
         lwz     r9,4(r9)                /* where to go when done */
+#ifdef CONFIG_TRACE_IRQFLAGS
+        lis     r12,reenable_mmu@h
+        ori     r12,r12,reenable_mmu@l
+        mtspr   SPRN_SRR0,r12
+        mtspr   SPRN_SRR1,r10
+        SYNC
+        RFI
+reenable_mmu:                           /* re-enable mmu so we can */
+        mfmsr   r10
+        lwz     r12,_MSR(r1)
+        xor     r10,r10,r12
+        andi.   r10,r10,MSR_EE          /* Did EE change? */
+        beq     1f
+
+        /* Save handler and return address into the 2 unused words
+         * of the STACK_FRAME_OVERHEAD (sneak sneak sneak). Everything
+         * else can be recovered from the pt_regs except r3 which for
+         * normal interrupts has been set to pt_regs and for syscalls
+         * is an argument, so we temporarily use ORIG_GPR3 to save it
+         */
+        stw     r9,8(r1)
+        stw     r11,12(r1)
+        stw     r3,ORIG_GPR3(r1)
+        bl      trace_hardirqs_off
+        lwz     r0,GPR0(r1)
+        lwz     r3,ORIG_GPR3(r1)
+        lwz     r4,GPR4(r1)
+        lwz     r5,GPR5(r1)
+        lwz     r6,GPR6(r1)
+        lwz     r7,GPR7(r1)
+        lwz     r8,GPR8(r1)
+        lwz     r9,8(r1)
+        lwz     r11,12(r1)
+1:      mtctr   r11
+        mtlr    r9
+        bctr                            /* jump to handler */
+#else /* CONFIG_TRACE_IRQFLAGS */
         mtspr   SPRN_SRR0,r11
         mtspr   SPRN_SRR1,r10
         mtlr    r9
         SYNC
         RFI                             /* jump to handler, enable MMU */
+#endif /* CONFIG_TRACE_IRQFLAGS */
 
 #if defined (CONFIG_6xx) || defined(CONFIG_E500)
 4:      rlwinm  r12,r12,0,~_TLF_NAPPING
@@ -251,6 +289,31 @@ _GLOBAL(DoSyscall)
 #ifdef SHOW_SYSCALLS
         bl      do_show_syscall
 #endif /* SHOW_SYSCALLS */
+#ifdef CONFIG_TRACE_IRQFLAGS
+        /* Return from syscalls can (and generally will) hard enable
+         * interrupts. You aren't supposed to call a syscall with
+         * interrupts disabled in the first place. However, to ensure
+         * that we get it right vs. lockdep if it happens, we force
+         * that hard enable here with appropriate tracing if we see
+         * that we have been called with interrupts off
+         */
+        mfmsr   r11
+        andi.   r12,r11,MSR_EE
+        bne+    1f
+        /* We came in with interrupts disabled, we enable them now */
+        bl      trace_hardirqs_on
+        mfmsr   r11
+        lwz     r0,GPR0(r1)
+        lwz     r3,GPR3(r1)
+        lwz     r4,GPR4(r1)
+        ori     r11,r11,MSR_EE
+        lwz     r5,GPR5(r1)
+        lwz     r6,GPR6(r1)
+        lwz     r7,GPR7(r1)
+        lwz     r8,GPR8(r1)
+        mtmsr   r11
+1:
+#endif /* CONFIG_TRACE_IRQFLAGS */
         rlwinm  r10,r1,0,0,(31-THREAD_SHIFT)    /* current_thread_info() */
         lwz     r11,TI_FLAGS(r10)
         andi.   r11,r11,_TIF_SYSCALL_T_OR_A
@@ -275,6 +338,7 @@ ret_from_syscall:
         rlwinm  r12,r1,0,0,(31-THREAD_SHIFT)    /* current_thread_info() */
         /* disable interrupts so current_thread_info()->flags can't change */
         LOAD_MSR_KERNEL(r10,MSR_KERNEL) /* doesn't include MSR_EE */
+        /* Note: We don't bother telling lockdep about it */
         SYNC
         MTMSRD(r10)
         lwz     r9,TI_FLAGS(r12)
@@ -288,6 +352,19 @@ ret_from_syscall:
         oris    r11,r11,0x1000  /* Set SO bit in CR */
         stw     r11,_CCR(r1)
 syscall_exit_cont:
+        lwz     r8,_MSR(r1)
+#ifdef CONFIG_TRACE_IRQFLAGS
+        /* If we are going to return from the syscall with interrupts
+         * off, we trace that here. It shouldn't happen though but we
+         * want to catch the bugger if it does right ?
+         */
+        andi.   r10,r8,MSR_EE
+        bne+    1f
+        stw     r3,GPR3(r1)
+        bl      trace_hardirqs_off
+        lwz     r3,GPR3(r1)
+1:
+#endif /* CONFIG_TRACE_IRQFLAGS */
 #if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
         /* If the process has its own DBCR0 value, load it up.  The internal
            debug mode bit tells us that dbcr0 should be loaded. */
@@ -311,7 +388,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
         mtlr    r4
         mtcr    r5
         lwz     r7,_NIP(r1)
-        lwz     r8,_MSR(r1)
         FIX_SRR1(r8, r0)
         lwz     r2,GPR2(r1)
         lwz     r1,GPR1(r1)
@@ -394,7 +470,9 @@ syscall_exit_work:
         andi.   r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP)
         beq     ret_from_except
 
-        /* Re-enable interrupts */
+        /* Re-enable interrupts. There is no need to trace that with
+         * lockdep as we are supposed to have IRQs on at this point
+         */
         ori     r10,r10,MSR_EE
         SYNC
         MTMSRD(r10)
@@ -705,6 +783,7 @@ ret_from_except:
         /* Hard-disable interrupts so that current_thread_info()->flags
          * can't change between when we test it and when we return
          * from the interrupt. */
+        /* Note: We don't bother telling lockdep about it */
         LOAD_MSR_KERNEL(r10,MSR_KERNEL)
         SYNC                    /* Some chip revs have problems here... */
         MTMSRD(r10)             /* disable interrupts */
@@ -744,11 +823,24 @@ resume_kernel:
         beq+    restore
         andi.   r0,r3,MSR_EE    /* interrupts off? */
         beq     restore         /* don't schedule if so */
+#ifdef CONFIG_TRACE_IRQFLAGS
+        /* Lockdep thinks irqs are enabled, we need to call
+         * preempt_schedule_irq with IRQs off, so we inform lockdep
+         * now that we -did- turn them off already
+         */
+        bl      trace_hardirqs_off
+#endif
 1:      bl      preempt_schedule_irq
         rlwinm  r9,r1,0,0,(31-THREAD_SHIFT)
         lwz     r3,TI_FLAGS(r9)
         andi.   r0,r3,_TIF_NEED_RESCHED
         bne-    1b
+#ifdef CONFIG_TRACE_IRQFLAGS
+        /* And now, to properly rebalance the above, we tell lockdep they
+         * are being turned back on, which will happen when we return
+         */
+        bl      trace_hardirqs_on
+#endif
 #else
 resume_kernel:
 #endif /* CONFIG_PREEMPT */
@@ -765,6 +857,28 @@ restore:
         stw     r6,icache_44x_need_flush@l(r4)
 1:
 #endif  /* CONFIG_44x */
+
+        lwz     r9,_MSR(r1)
+#ifdef CONFIG_TRACE_IRQFLAGS
+        /* Lockdep doesn't know about the fact that IRQs are temporarily turned
+         * off in this assembly code while peeking at TI_FLAGS() and such. However
+         * we need to inform it if the exception turned interrupts off, and we
+         * are about to trun them back on.
+         *
+         * The problem here sadly is that we don't know whether the exceptions was
+         * one that turned interrupts off or not. So we always tell lockdep about
+         * turning them on here when we go back to wherever we came from with EE
+         * on, even if that may meen some redudant calls being tracked. Maybe later
+         * we could encode what the exception did somewhere or test the exception
+         * type in the pt_regs but that sounds overkill
+         */
+        andi.   r10,r9,MSR_EE
+        beq     1f
+        bl      trace_hardirqs_on
+        lwz     r9,_MSR(r1)
+1:
+#endif /* CONFIG_TRACE_IRQFLAGS */
+
         lwz     r0,GPR0(r1)
         lwz     r2,GPR2(r1)
         REST_4GPRS(3, r1)
@@ -782,7 +896,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
         stwcx.  r0,0,r1                 /* to clear the reservation */
 
 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
-        lwz     r9,_MSR(r1)
         andi.   r10,r9,MSR_RI           /* check if this exception occurred */
         beql    nonrecoverable          /* at a bad place (MSR:RI = 0) */
 
@@ -805,7 +918,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
         MTMSRD(r10)             /* clear the RI bit */
         .globl exc_exit_restart
 exc_exit_restart:
-        lwz     r9,_MSR(r1)
         lwz     r12,_NIP(r1)
         FIX_SRR1(r9,r10)
         mtspr   SPRN_SRR0,r12
@@ -1035,11 +1147,18 @@ do_work:			/* r10 contains MSR_KERNEL here */
         beq     do_user_signal
 
 do_resched:                     /* r10 contains MSR_KERNEL here */
+        /* Note: We don't need to inform lockdep that we are enabling
+         * interrupts here. As far as it knows, they are already enabled
+         */
         ori     r10,r10,MSR_EE
         SYNC
         MTMSRD(r10)             /* hard-enable interrupts */
         bl      schedule
 recheck:
+        /* Note: And we don't tell it we are disabling them again
+         * neither. Those disable/enable cycles used to peek at
+         * TI_FLAGS aren't advertised.
+         */
         LOAD_MSR_KERNEL(r10,MSR_KERNEL)
         SYNC
         MTMSRD(r10)             /* disable interrupts */
diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
index 1d154248cf40..e1e3059cf34b 100644
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -119,6 +119,8 @@ notrace unsigned long __init early_init(unsigned long dt_ptr)
  */
 notrace void __init machine_init(unsigned long dt_ptr)
 {
+        lockdep_init();
+
         /* Enable early debugging if any specified (see udbg.h) */
         udbg_early_init();