powerpc/64s/exception: Remove lite interrupt return

Regular interrupt return restores NVGPRS whereas lite returns do not.
This is clumsy: most interrupts can return without restoring NVGPRS in
most of the time, but there are special cases that require it (when
registers have been modified by the kernel). So change interrupt
return to not restore NVGPRS, and have interrupt handlers restore them
explicitly in the cases that requires it.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200225173541.1549955-30-npiggin@gmail.com

arch/powerpc/kernel/entry_64.S

@@ -479,12 +479,6 @@ _ASM_NOKPROBE_SYMBOL(fast_interrupt_return)
 	.globl interrupt_return
 interrupt_return:
 _ASM_NOKPROBE_SYMBOL(interrupt_return)
-	REST_NVGPRS(r1)
-
-	.balign IFETCH_ALIGN_BYTES
-	.globl interrupt_return_lite
-interrupt_return_lite:
-_ASM_NOKPROBE_SYMBOL(interrupt_return_lite)
 	ld	r4,_MSR(r1)
 	andi.	r0,r4,MSR_PR
 	beq	.Lkernel_interrupt_return

arch/powerpc/kernel/exceptions-64s.S

@@ -1529,7 +1529,7 @@ EXC_COMMON_BEGIN(hardware_interrupt_common)
 	RUNLATCH_ON
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	do_IRQ
-	b	interrupt_return_lite
+	b	interrupt_return
 
 	GEN_KVM hardware_interrupt
 
@@ -1557,6 +1557,7 @@ EXC_COMMON_BEGIN(alignment_common)
 	GEN_COMMON alignment
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	alignment_exception
+	REST_NVGPRS(r1) /* instruction emulation may change GPRs */
 	b	interrupt_return
 
 	GEN_KVM alignment
@@ -1620,6 +1621,7 @@ EXC_COMMON_BEGIN(program_check_common)
 3:
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	program_check_exception
+	REST_NVGPRS(r1) /* instruction emulation may change GPRs */
 	b	interrupt_return
 
 	GEN_KVM program_check
@@ -1716,7 +1718,7 @@ EXC_COMMON_BEGIN(decrementer_common)
 	RUNLATCH_ON
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	timer_interrupt
-	b	interrupt_return_lite
+	b	interrupt_return
 
 	GEN_KVM decrementer
 
@@ -1807,7 +1809,7 @@ EXC_COMMON_BEGIN(doorbell_super_common)
 #else
 	bl	unknown_exception
 #endif
-	b	interrupt_return_lite
+	b	interrupt_return
 
 	GEN_KVM doorbell_super
 
@@ -2076,6 +2078,7 @@ EXC_COMMON_BEGIN(emulation_assist_common)
 	GEN_COMMON emulation_assist
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	emulation_assist_interrupt
+	REST_NVGPRS(r1) /* instruction emulation may change GPRs */
 	b	interrupt_return
 
 	GEN_KVM emulation_assist
@@ -2194,7 +2197,7 @@ EXC_COMMON_BEGIN(h_doorbell_common)
 #else
 	bl	unknown_exception
 #endif
-	b	interrupt_return_lite
+	b	interrupt_return
 
 	GEN_KVM h_doorbell
 
@@ -2224,7 +2227,7 @@ EXC_COMMON_BEGIN(h_virt_irq_common)
 	RUNLATCH_ON
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	do_IRQ
-	b	interrupt_return_lite
+	b	interrupt_return
 
 	GEN_KVM h_virt_irq
 
@@ -2271,7 +2274,7 @@ EXC_COMMON_BEGIN(performance_monitor_common)
 	RUNLATCH_ON
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	performance_monitor_exception
-	b	interrupt_return_lite
+	b	interrupt_return
 
 	GEN_KVM performance_monitor
 
@@ -2668,6 +2671,7 @@ EXC_COMMON_BEGIN(altivec_assist_common)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 #ifdef CONFIG_ALTIVEC
 	bl	altivec_assist_exception
+	REST_NVGPRS(r1) /* instruction emulation may change GPRs */
 #else
 	bl	unknown_exception
 #endif
@@ -3057,7 +3061,7 @@ do_hash_page:
         cmpdi	r3,0			/* see if __hash_page succeeded */
 
 	/* Success */
-	beq	interrupt_return_lite	/* Return from exception on success */
+	beq	interrupt_return	/* Return from exception on success */
 
 	/* Error */
 	blt-	13f
@@ -3074,7 +3078,7 @@ handle_page_fault:
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	do_page_fault
 	cmpdi	r3,0
-	beq+	interrupt_return_lite
+	beq+	interrupt_return
 	mr	r5,r3
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	ld	r4,_DAR(r1)
@@ -3089,9 +3093,9 @@ handle_dabr_fault:
 	bl      do_break
 	/*
 	 * do_break() may have changed the NV GPRS while handling a breakpoint.
-	 * If so, we need to restore them with their updated values. Don't use
-	 * interrupt_return_lite here.
+	 * If so, we need to restore them with their updated values.
 	 */
+	REST_NVGPRS(r1)
 	b       interrupt_return