ARM: 8150/3: fiq: Replace default FIQ handler

This patch introduces a new default FIQ handler that is structured in a
similar way to the existing ARM exception handler and result in the FIQ
being handled by C code running on the SVC stack (despite this code run
in the FIQ handler is subject to severe limitations with respect to
locking making normal interaction with the kernel impossible).

This default handler allows concepts that on x86 would be handled using
NMIs to be realized on ARM.

Credit:

    This patch is a near complete re-write of a patch originally
    provided by Anton Vorontsov. Today only a couple of small fragments
    survive, however without Anton's work to build from this patch would
    not exist. Thanks also to Russell King for spoonfeeding me a variety
    of fixes during the review cycle.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 87 insertions, 11 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 36276cdccfbc..859f56cb122b 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -146,7 +146,7 @@ ENDPROC(__und_invalid)
 #define SPFIX(code...)
 #endif
 
-	.macro	svc_entry, stack_hole=0
+	.macro	svc_entry, stack_hole=0, trace=1
  UNWIND(.fnstart		)
  UNWIND(.save {r0 - pc}		)
 	sub	sp, sp, #(S_FRAME_SIZE + \stack_hole - 4)
@@ -182,9 +182,11 @@ ENDPROC(__und_invalid)
 	@
 	stmia	r7, {r2 - r6}
 
+	.if \trace
 #ifdef CONFIG_TRACE_IRQFLAGS
 	bl	trace_hardirqs_off
 #endif
+	.endif
 	.endm
 
 	.align	5
@@ -295,6 +297,15 @@ __pabt_svc:
 ENDPROC(__pabt_svc)
 
 	.align	5
+__fiq_svc:
+	svc_entry trace=0
+	mov	r0, sp				@ struct pt_regs *regs
+	bl	handle_fiq_as_nmi
+	svc_exit_via_fiq
+ UNWIND(.fnend		)
+ENDPROC(__fiq_svc)
+
+	.align	5
 .LCcralign:
 	.word	cr_alignment
 #ifdef MULTI_DABORT
@@ -305,6 +316,46 @@ ENDPROC(__pabt_svc)
 	.word	fp_enter
 
 /*
+ * Abort mode handlers
+ */
+
+@
+@ Taking a FIQ in abort mode is similar to taking a FIQ in SVC mode
+@ and reuses the same macros. However in abort mode we must also
+@ save/restore lr_abt and spsr_abt to make nested aborts safe.
+@
+	.align 5
+__fiq_abt:
+	svc_entry trace=0
+
+ ARM(	msr	cpsr_c, #ABT_MODE | PSR_I_BIT | PSR_F_BIT )
+ THUMB( mov	r0, #ABT_MODE | PSR_I_BIT | PSR_F_BIT )
+ THUMB( msr	cpsr_c, r0 )
+	mov	r1, lr		@ Save lr_abt
+	mrs	r2, spsr	@ Save spsr_abt, abort is now safe
+ ARM(	msr	cpsr_c, #SVC_MODE | PSR_I_BIT | PSR_F_BIT )
+ THUMB( mov	r0, #SVC_MODE | PSR_I_BIT | PSR_F_BIT )
+ THUMB( msr	cpsr_c, r0 )
+	stmfd	sp!, {r1 - r2}
+
+	add	r0, sp, #8			@ struct pt_regs *regs
+	bl	handle_fiq_as_nmi
+
+	ldmfd	sp!, {r1 - r2}
+ ARM(	msr	cpsr_c, #ABT_MODE | PSR_I_BIT | PSR_F_BIT )
+ THUMB( mov	r0, #ABT_MODE | PSR_I_BIT | PSR_F_BIT )
+ THUMB( msr	cpsr_c, r0 )
+	mov	lr, r1		@ Restore lr_abt, abort is unsafe
+	msr	spsr_cxsf, r2	@ Restore spsr_abt
+ ARM(	msr	cpsr_c, #SVC_MODE | PSR_I_BIT | PSR_F_BIT )
+ THUMB( mov	r0, #SVC_MODE | PSR_I_BIT | PSR_F_BIT )
+ THUMB( msr	cpsr_c, r0 )
+
+	svc_exit_via_fiq
+ UNWIND(.fnend		)
+ENDPROC(__fiq_abt)
+
+/*
  * User mode handlers
  *
  * EABI note: sp_svc is always 64-bit aligned here, so should S_FRAME_SIZE
@@ -314,7 +365,7 @@ ENDPROC(__pabt_svc)
 #error "sizeof(struct pt_regs) must be a multiple of 8"
 #endif
 
-	.macro	usr_entry
+	.macro	usr_entry, trace=1
  UNWIND(.fnstart	)
  UNWIND(.cantunwind	)	@ don't unwind the user space
 	sub	sp, sp, #S_FRAME_SIZE
@@ -351,10 +402,12 @@ ENDPROC(__pabt_svc)
 	@
 	zero_fp
 
+	.if	\trace
 #ifdef CONFIG_IRQSOFF_TRACER
 	bl	trace_hardirqs_off
 #endif
 	ct_user_exit save = 0
+	.endif
 	.endm
 
 	.macro	kuser_cmpxchg_check
@@ -683,6 +736,17 @@ ENTRY(ret_from_exception)
 ENDPROC(__pabt_usr)
 ENDPROC(ret_from_exception)
 
+	.align	5
+__fiq_usr:
+	usr_entry trace=0
+	kuser_cmpxchg_check
+	mov	r0, sp				@ struct pt_regs *regs
+	bl	handle_fiq_as_nmi
+	get_thread_info tsk
+	restore_user_regs fast = 0, offset = 0
+ UNWIND(.fnend		)
+ENDPROC(__fiq_usr)
+
 /*
  * Register switch for ARMv3 and ARMv4 processors
  * r0 = previous task_struct, r1 = previous thread_info, r2 = next thread_info
@@ -1118,17 +1182,29 @@ vector_addrexcptn:
 	b	vector_addrexcptn
 
 /*=============================================================================
- * Undefined FIQs
+ * FIQ "NMI" handler
  *-----------------------------------------------------------------------------
- * Enter in FIQ mode, spsr = ANY CPSR, lr = ANY PC
- * MUST PRESERVE SVC SPSR, but need to switch to SVC mode to show our msg.
- * Basically to switch modes, we *HAVE* to clobber one register...  brain
- * damage alert!  I don't think that we can execute any code in here in any
- * other mode than FIQ...  Ok you can switch to another mode, but you can't
- * get out of that mode without clobbering one register.
+ * Handle a FIQ using the SVC stack allowing FIQ act like NMI on x86
+ * systems.
  */
-vector_fiq:
-	subs	pc, lr, #4
+	vector_stub	fiq, FIQ_MODE, 4
+
+	.long	__fiq_usr			@  0  (USR_26 / USR_32)
+	.long	__fiq_svc			@  1  (FIQ_26 / FIQ_32)
+	.long	__fiq_svc			@  2  (IRQ_26 / IRQ_32)
+	.long	__fiq_svc			@  3  (SVC_26 / SVC_32)
+	.long	__fiq_svc			@  4
+	.long	__fiq_svc			@  5
+	.long	__fiq_svc			@  6
+	.long	__fiq_abt			@  7
+	.long	__fiq_svc			@  8
+	.long	__fiq_svc			@  9
+	.long	__fiq_svc			@  a
+	.long	__fiq_svc			@  b
+	.long	__fiq_svc			@  c
+	.long	__fiq_svc			@  d
+	.long	__fiq_svc			@  e
+	.long	__fiq_svc			@  f
 
 	.globl	vector_fiq_offset
 	.equ	vector_fiq_offset, vector_fiq