powerpc: Rework lazy-interrupt handling

From 0ace17ba6960a8788b1bda3770df254cbbc6a244 Mon Sep 17 00:00:00 2001

From 0ace17ba6960a8788b1bda3770df254cbbc6a244 Mon Sep 17 00:00:00 2001
From: Benjamin Herrenschmidt<[email protected]>
Date: Thu, 9 Feb 2012 15:25:04 +1100
Subject: [PATCH] powerpc: Rework lazy-interrupt handling

The current implementation of lazy interrupts handling has some issues that this tries to address.

Except on iSeries, we don't do the various workarounds we need to do on re-enable when returning from an interrupt, which can do an implicit re-enable, and thus we may still lose or get delayed decrementer or doorbell interrupts.

The current scheme also makes it much harder to handle the external "edge" interrupts provided by some BookE processors when using the EPR facility (External Proxy) and the Freescale Hypervisor.

We also hard mask on decrementer interrupts which is sub-optimal.

This is an attempt at fixing it all in one go by reworking the way we do the lazy interrupt disabling.

The base idea is to replace the "hard_enabled" field with a "irq_happened" field in which we store a bit mask of what interrupt occurred while soft-disabled.

When re-enabling, either via arch_local_irq_restore() or when returning from an interrupt, we can now decide what to do by testing bits in that field. We then implement re-emitting of the lost interrupts via either a re-use of the existing exception frame (exception exit case) or via the creation of a new one from assembly code (arch_local_irq_enable), without the need to trigger a fake one using set_dec() or similar.

In addition, this adds a few refinements:

- We no longer hard disable decrementer interrupts that occur
while soft-disabled. We now simply bump the decrementer back to max (on BookS) or leave it stopped (on BookE) and continue with hard interrupts enabled, which means that we'll potentially get better sample quality from performance monitor interrupts.

- Timer, decrementer and doorbell interrupts now hard-enable
shortly after removing the source of the interrupt, which means they no longer run entirely hard disabled. Again, this will improve perf sample quality.

- On Book3E 64-bit, we now make the performance monitor interrupt
act as an NMI like Book3S (the necessary C code for that to work appear to already be present in the FSL perf code, notably calling nmi_enter instead of irq_enter).

There are additional refinements that we can do on top of this patch:

- We could remove the ps3 workaround from arch_local_irq_enable(),
I believe that it should no longer be necessary

- We could make "masked" decrementer interrupts act as NMIs when doing
timer-based perf sampling to improve the sample quality.

- There are additional simplifications of the exception entry/exit path
that I've spotted along the way, such as merging fast_exception_return with the normal code path.

This patch needs a LOT more testing& review than it had so far !!!

Not-signed-off-by-yet: Benjamin Herrenschmidt<[email protected]>
---

v2:

- Add hard-enable to decrementer, timer and doorbells
- Fix CR clobber in masked irq handling on BookE
- Make embedded perf interrupt act as an NMI
- Add a PACA_HAPPENED_EE_EDGE for use by FSL if they want to retrigger an interrupt without preventing hard-enable

Signed-off-by Benjamin Herrenschmidt<[email protected]>

---
  arch/powerpc/include/asm/exception-64s.h        |   21 ++-
  arch/powerpc/include/asm/hw_irq.h               |   51 +++++-
  arch/powerpc/include/asm/irqflags.h             |   13 +-
  arch/powerpc/include/asm/paca.h                 |    2 +-
  arch/powerpc/kernel/asm-offsets.c               |    2 +-
  arch/powerpc/kernel/dbell.c                     |   12 ++
  arch/powerpc/kernel/entry_64.S                  |   96 ++++++-----
  arch/powerpc/kernel/exceptions-64e.S            |  210 ++++++++++++++++-------
  arch/powerpc/kernel/exceptions-64s.S            |   90 ++++++----
  arch/powerpc/kernel/head_64.S                   |    9 -
  arch/powerpc/kernel/idle_book3e.S               |    8 +-
  arch/powerpc/kernel/idle_power4.S               |   17 ++-
  arch/powerpc/kernel/idle_power7.S               |   20 ++-
  arch/powerpc/kernel/irq.c                       |  187 ++++++++++++++------
  arch/powerpc/kernel/time.c                      |   15 ++-
  arch/powerpc/platforms/iseries/Makefile         |    2 +-
  arch/powerpc/platforms/iseries/exception.S      |   11 +-
  arch/powerpc/platforms/iseries/misc.S           |   26 ---
  arch/powerpc/platforms/pseries/processor_idle.c |   24 +++-
  19 files changed, 540 insertions(+), 276 deletions(-)

delete mode 100644 arch/powerpc/platforms/iseries/misc.S

arch/powerpc/kernel/exceptions-64e.S +97 -60

index 429983c..7fa4096 100644
@@ -21,6 +21,7 @@
  #include<asm/exception-64e.h>
  #include<asm/bug.h>
  #include<asm/irqflags.h>
+#include<asm/hw_irq.h>
  #include<asm/ptrace.h>
  #include<asm/ppc-opcode.h>
  #include<asm/mmu.h>

@@ -77,59 +78,55 @@
  #define SPRN_MC_SRR1	SPRN_MCSRR1
 
  #define NORMAL_EXCEPTION_PROLOG(n, addition)				    \
-	EXCEPTION_PROLOG(n, GEN, addition##_GEN)
+	EXCEPTION_PROLOG(n, GEN, addition##_GEN(n))
 
  #define CRIT_EXCEPTION_PROLOG(n, addition)				    \
-	EXCEPTION_PROLOG(n, CRIT, addition##_CRIT)
+	EXCEPTION_PROLOG(n, CRIT, addition##_CRIT(n))
 
  #define DBG_EXCEPTION_PROLOG(n, addition)				    \
-	EXCEPTION_PROLOG(n, DBG, addition##_DBG)
+	EXCEPTION_PROLOG(n, DBG, addition##_DBG(n))
 
  #define MC_EXCEPTION_PROLOG(n, addition)				    \
-	EXCEPTION_PROLOG(n, MC, addition##_MC)
+	EXCEPTION_PROLOG(n, MC, addition##_MC(n))
 
 
  /* Variants of the "addition" argument for the prolog
   */
-#define PROLOG_ADDITION_NONE_GEN
-#define PROLOG_ADDITION_NONE_CRIT
-#define PROLOG_ADDITION_NONE_DBG
-#define PROLOG_ADDITION_NONE_MC
+#define PROLOG_ADDITION_NONE_GEN(n)
+#define PROLOG_ADDITION_NONE_CRIT(n)
+#define PROLOG_ADDITION_NONE_DBG(n)
+#define PROLOG_ADDITION_NONE_MC(n)
 
-#define PROLOG_ADDITION_MASKABLE_GEN					    \
+#define PROLOG_ADDITION_MASKABLE_GEN(n)					    \
  	lbz	r11,PACASOFTIRQEN(r13); /* are irqs soft-disabled ? */	    \
  	cmpwi	cr0,r11,0;		/* yes ->  go out of line */	    \
-	beq	masked_interrupt_book3e;
+	beq	masked_interrupt_book3e_##n;
 
-#define PROLOG_ADDITION_2REGS_GEN					    \
+#define PROLOG_ADDITION_2REGS_GEN(n)					    \
  	std	r14,PACA_EXGEN+EX_R14(r13);				    \
  	std	r15,PACA_EXGEN+EX_R15(r13)
 
-#define PROLOG_ADDITION_1REG_GEN					    \
+#define PROLOG_ADDITION_1REG_GEN(n)					    \
  	std	r14,PACA_EXGEN+EX_R14(r13);
 
-#define PROLOG_ADDITION_2REGS_CRIT					    \
+#define PROLOG_ADDITION_2REGS_CRIT(n)					    \
  	std	r14,PACA_EXCRIT+EX_R14(r13);				    \
  	std	r15,PACA_EXCRIT+EX_R15(r13)
 
-#define PROLOG_ADDITION_2REGS_DBG					    \
+#define PROLOG_ADDITION_2REGS_DBG(n)					    \
  	std	r14,PACA_EXDBG+EX_R14(r13);				    \
  	std	r15,PACA_EXDBG+EX_R15(r13)
 
-#define PROLOG_ADDITION_2REGS_MC					    \
+#define PROLOG_ADDITION_2REGS_MC(n)					    \
  	std	r14,PACA_EXMC+EX_R14(r13);				    \
  	std	r15,PACA_EXMC+EX_R15(r13)
 
-#define PROLOG_ADDITION_DOORBELL_GEN					    \
-	lbz	r11,PACASOFTIRQEN(r13); /* are irqs soft-disabled ? */	    \
-	cmpwi	cr0,r11,0;		/* yes ->  go out of line */	    \
-	beq	masked_doorbell_book3e
-
 
  /* Core exception code for all exceptions except TLB misses.
   * XXX: Needs to make SPRN_SPRG_GEN depend on exception type
   */
  #define EXCEPTION_COMMON(n, excf, ints)					    \
+exc_##n##_common:							    \
  	std	r0,GPR0(r1);		/* save r0 in stackframe */	    \
  	std	r2,GPR2(r1);		/* save r2 in stackframe */	    \
  	SAVE_4GPRS(3, r1);		/* save r3 - r6 in stackframe */    \

@@ -167,19 +164,25 @@
  	std	r0,RESULT(r1);		/* clear regs->result */	    \
  	ints;
 
-/* Variants for the "ints" argument */
-#define INTS_KEEP
-#define INTS_DISABLE_SOFT						    \
+/* Variants for the "ints" argument. We know r0 is 0 on entry */
+#define INTS_KEEP							    \
  	stb	r0,PACASOFTIRQEN(r13);	/* mark interrupts soft-disabled */ \
  	TRACE_DISABLE_INTS;
-#define INTS_DISABLE_HARD						    \
-	stb	r0,PACAHARDIRQEN(r13); /* and hard disabled */
-#define INTS_DISABLE_ALL						    \
-	INTS_DISABLE_SOFT						    \
-	INTS_DISABLE_HARD
-
-/* This is called by exceptions that used INTS_KEEP (that is did not clear
- * neither soft nor hard IRQ indicators in the PACA. This will restore MSR:EE
+
+/* This second version is meant for exceptions that don't immediately
+ * hard-enable. We set a bit in paca->irq_happened to ensure that
+ * a subsequent call to arch_local_irq_restore() will properly
+ * hard-enable and avoid the fast-path
+ */
+#define INTS_DISABLE							    \
+	stb	r0,PACASOFTIRQEN(r13);	/* mark interrupts soft-disabled */ \
+	lbz	r0,PACAIRQHAPPENED(r13);				    \
+	ori	r0,r0,PACA_HAPPENED;					    \
+	stb	r0,PACAIRQHAPPENED(r13);				    \
+	TRACE_DISABLE_INTS;
+
+/* This is called by exceptions that used INTS_KEEP (that is did
+ * not set hard IRQ indicators in the PACA). This will restore MSR:EE
   * to it's previous value
   *
   * XXX In the long run, we may want to open-code it in order to separate the

@@ -238,7 +241,7 @@ exc_##n##_bad_stack:							    \
  #define MASKABLE_EXCEPTION(trapnum, label, hdlr, ack)			\
  	START_EXCEPTION(label);						\
  	NORMAL_EXCEPTION_PROLOG(trapnum, PROLOG_ADDITION_MASKABLE)	\
-	EXCEPTION_COMMON(trapnum, PACA_EXGEN, INTS_DISABLE_ALL)		\
+	EXCEPTION_COMMON(trapnum, PACA_EXGEN, INTS_DISABLE)		\
  	ack(r8);							\
  	CHECK_NAPPING();						\
  	addi	r3,r1,STACK_FRAME_OVERHEAD;				\

@@ -289,7 +292,7 @@ interrupt_end_book3e:
  /* Critical Input Interrupt */
  	START_EXCEPTION(critical_input);
  	CRIT_EXCEPTION_PROLOG(0x100, PROLOG_ADDITION_NONE)
-//	EXCEPTION_COMMON(0x100, PACA_EXCRIT, INTS_DISABLE_ALL)
+//	EXCEPTION_COMMON(0x100, PACA_EXCRIT, INTS_DISABLE)
  //	bl	special_reg_save_crit
  //	CHECK_NAPPING();
  //	addi	r3,r1,STACK_FRAME_OVERHEAD

@@ -300,7 +303,7 @@ interrupt_end_book3e:
  /* Machine Check Interrupt */
  	START_EXCEPTION(machine_check);
  	CRIT_EXCEPTION_PROLOG(0x200, PROLOG_ADDITION_NONE)
-//	EXCEPTION_COMMON(0x200, PACA_EXMC, INTS_DISABLE_ALL)
+//	EXCEPTION_COMMON(0x200, PACA_EXMC, INTS_DISABLE)
  //	bl	special_reg_save_mc
  //	addi	r3,r1,STACK_FRAME_OVERHEAD
  //	CHECK_NAPPING();

@@ -339,7 +342,7 @@ interrupt_end_book3e:
  	START_EXCEPTION(program);
  	NORMAL_EXCEPTION_PROLOG(0x700, PROLOG_ADDITION_1REG)
  	mfspr	r14,SPRN_ESR
-	EXCEPTION_COMMON(0x700, PACA_EXGEN, INTS_DISABLE_SOFT)
+	EXCEPTION_COMMON(0x700, PACA_EXGEN, INTS_KEEP)
  	std	r14,_DSISR(r1)
  	addi	r3,r1,STACK_FRAME_OVERHEAD
  	ld	r14,PACA_EXGEN+EX_R14(r13)

@@ -372,7 +375,7 @@ interrupt_end_book3e:
  /* Watchdog Timer Interrupt */
  	START_EXCEPTION(watchdog);
  	CRIT_EXCEPTION_PROLOG(0x9f0, PROLOG_ADDITION_NONE)
-//	EXCEPTION_COMMON(0x9f0, PACA_EXCRIT, INTS_DISABLE_ALL)
+//	EXCEPTION_COMMON(0x9f0, PACA_EXCRIT, INTS_DISABLE)
  //	bl	special_reg_save_crit
  //	CHECK_NAPPING();
  //	addi	r3,r1,STACK_FRAME_OVERHEAD

@@ -450,7 +453,7 @@ interrupt_end_book3e:
  	mfspr	r15,SPRN_SPRG_CRIT_SCRATCH
  	mtspr	SPRN_SPRG_GEN_SCRATCH,r15
  	mfspr	r14,SPRN_DBSR
-	EXCEPTION_COMMON(0xd00, PACA_EXCRIT, INTS_DISABLE_ALL)
+	EXCEPTION_COMMON(0xd00, PACA_EXCRIT, INTS_DISABLE)
  	std	r14,_DSISR(r1)
  	addi	r3,r1,STACK_FRAME_OVERHEAD
  	mr	r4,r14

@@ -515,7 +518,7 @@ kernel_dbg_exc:
  	mfspr	r15,SPRN_SPRG_DBG_SCRATCH
  	mtspr	SPRN_SPRG_GEN_SCRATCH,r15
  	mfspr	r14,SPRN_DBSR
-	EXCEPTION_COMMON(0xd00, PACA_EXDBG, INTS_DISABLE_ALL)
+	EXCEPTION_COMMON(0xd08, PACA_EXDBG, INTS_DISABLE)
  	std	r14,_DSISR(r1)
  	addi	r3,r1,STACK_FRAME_OVERHEAD
  	mr	r4,r14

@@ -525,21 +528,22 @@ kernel_dbg_exc:
  	bl	.DebugException
  	b	.ret_from_except
 
-	MASKABLE_EXCEPTION(0x260, perfmon, .performance_monitor_exception, ACK_NONE)
+	START_EXCEPTION(perfmon);
+	NORMAL_EXCEPTION_PROLOG(0x260, PROLOG_ADDITION_NONE)
+	EXCEPTION_COMMON(0x260, PACA_EXGEN, INTS_DISABLE)
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+	ld	r14,PACA_EXGEN+EX_R14(r13)
+	bl	.save_nvgprs
+	bl	.performance_monitor_exception
+	b	.ret_from_except
 
  /* Doorbell interrupt */
-	START_EXCEPTION(doorbell)
-	NORMAL_EXCEPTION_PROLOG(0x2070, PROLOG_ADDITION_DOORBELL)
-	EXCEPTION_COMMON(0x2070, PACA_EXGEN, INTS_DISABLE_ALL)
-	CHECK_NAPPING()
-	addi	r3,r1,STACK_FRAME_OVERHEAD
-	bl	.doorbell_exception
-	b	.ret_from_except_lite
+	MASKABLE_EXCEPTION(0x280, doorbell, .doorbell_exception, ACK_NONE)
 
  /* Doorbell critical Interrupt */
  	START_EXCEPTION(doorbell_crit);
-	CRIT_EXCEPTION_PROLOG(0x2080, PROLOG_ADDITION_NONE)
-//	EXCEPTION_COMMON(0x2080, PACA_EXCRIT, INTS_DISABLE_ALL)
+	CRIT_EXCEPTION_PROLOG(0x2a0, PROLOG_ADDITION_NONE)
+//	EXCEPTION_COMMON(0x280, PACA_EXCRIT, INTS_DISABLE)
  //	bl	special_reg_save_crit
  //	CHECK_NAPPING();
  //	addi	r3,r1,STACK_FRAME_OVERHEAD

@@ -547,38 +551,116 @@ kernel_dbg_exc:
  //	b	ret_from_crit_except
  	b	.
 
+/* Guest Doorbell */
  	MASKABLE_EXCEPTION(0x2c0, guest_doorbell, .unknown_exception, ACK_NONE)
-	MASKABLE_EXCEPTION(0x2e0, guest_doorbell_crit, .unknown_exception, ACK_NONE)
-	MASKABLE_EXCEPTION(0x310, hypercall, .unknown_exception, ACK_NONE)
-	MASKABLE_EXCEPTION(0x320, ehpriv, .unknown_exception, ACK_NONE)
+
+/* Guest Doorbell critical Interrupt */
+	START_EXCEPTION(guest_doorbell_crit);
+	CRIT_EXCEPTION_PROLOG(0x2e0, PROLOG_ADDITION_NONE)
+//	EXCEPTION_COMMON(0x2e0, PACA_EXCRIT, INTS_DISABLE)
+//	bl	special_reg_save_crit
+//	CHECK_NAPPING();
+//	addi	r3,r1,STACK_FRAME_OVERHEAD
+//	bl	.guest_doorbell_critical_exception
+//	b	ret_from_crit_except
+	b	.
+
+/* Hypervisor call */
+	START_EXCEPTION(hypercall);
+	NORMAL_EXCEPTION_PROLOG(0x310, PROLOG_ADDITION_NONE)
+	EXCEPTION_COMMON(0x310, PACA_EXGEN, INTS_KEEP)
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+	bl	.save_nvgprs
+	INTS_RESTORE_HARD
+	bl	.unknown_exception
+	b	.ret_from_except
+
+/* Embedded Hypervisor priviledged  */
+	START_EXCEPTION(ehpriv);
+	NORMAL_EXCEPTION_PROLOG(0x320, PROLOG_ADDITION_NONE)
+	EXCEPTION_COMMON(0x320, PACA_EXGEN, INTS_KEEP)
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+	bl	.save_nvgprs
+	INTS_RESTORE_HARD
+	bl	.unknown_exception
+	b	.ret_from_except
 
 
  /*
- * An interrupt came in while soft-disabled; clear EE in SRR1,
- * clear paca->hard_enabled and return.
+ * An interrupt came in while soft-disabled; We mark paca->irq_happened
+ * accordingly and if the interrupt is level sensitive, we hard disable
   */
-masked_doorbell_book3e:
-	mtcr	r10
-	/* Resend the doorbell to fire again when ints enabled */
-	mfspr	r10,SPRN_PIR
-	PPC_MSGSND(r10)
-	b	masked_interrupt_book3e_common
 
-masked_interrupt_book3e:
+masked_interrupt_book3e_0x500:
+	li	r11,PACA_HAPPENED_EE
+	b	masked_interrupt_book3e_full_mask
+
+masked_interrupt_book3e_0x900:
+	ACK_DEC(r11);
+	li	r11,PACA_HAPPENED_DEC
+	b	masked_interrupt_book3e_no_mask
+masked_interrupt_book3e_0x980:
+	ACK_FIT(r11);
+	li	r11,PACA_HAPPENED_DEC

arch/powerpc/kernel/exceptions-64e.S +33 -1

+	stb	r10,PACAIRQHAPPENED(r13)
  	mfspr	r10,SPRN_SRR1
  	rldicl	r11,r10,48,1		/* clear MSR_EE */
  	rotldi	r10,r11,16
  	mtspr	SPRN_SRR1,r10
-	ld	r10,PACA_EXGEN+EX_R10(r13);	/* restore registers */
+1:	ld	r10,PACA_EXGEN+EX_R10(r13);
  	ld	r11,PACA_EXGEN+EX_R11(r13);
  	mfspr	r13,SPRN_SPRG_GEN_SCRATCH;
  	rfi
  	b	.
 
  /*
+ * Called from arch_local_irq_enable when an interrupt needs
+ * to be resent. r3 contains either 0x500,0x900,0x260 or 0x280
+ * to indicate the kind of interrupt. MSR:EE is already off.
+ * We generate a stackframe like if a real interrupt had happened.
+ *
+ * Note: While MSR:EE is off, we need to make sure that _MSR
+ * in the generated frame has EE set to 1 or the exception
+ * handler will not properly re-enable them.
+ */
+_GLOBAL(__reemit_interrupt)
+	/* We are going to jump to the exception common code which
+	 * will retrieve various register values from the PACA which
+	 * we don't give a damn about.
+	 */
+	mflr	r10
+	mfmsr	r11
+	mfcr	r4;
+	mtspr	SPRN_SPRG_GEN_SCRATCH,r13;
+	std	r1,PACA_EXGEN+EX_R1(r13);
+	stw	r4,PACA_EXGEN+EX_CR(r13);
+	ori	r11,r11,MSR_EE
+	subi	r1,r1,INT_FRAME_SIZE;
+	cmpwi	cr0,r3,0x500
+	beq	exc_0x500_common
+	cmpwi	cr0,r3,0x900
+	beq+	exc_0x900_common
+	cmpwi	cr0,r3,0x280
+	beq+	exc_0x280_common
+	blr
+
+/*
   * This is called from 0x300 and 0x400 handlers after the prologs with
   * r14 and r15 containing the fault address and error code, with the
   * original values stashed away in the PACA

Quoted 11 lines

arch/powerpc/kernel/exceptions-64e.S +11 -0

+masked_interrupt_book3e_0x900:
+	ACK_DEC(r11);
+	li	r11,PACA_HAPPENED_DEC
+	b	masked_interrupt_book3e_no_mask
+masked_interrupt_book3e_0x980:
+	ACK_FIT(r11);
+	li	r11,PACA_HAPPENED_DEC
+	b	masked_interrupt_book3e_no_mask
+masked_interrupt_book3e_0x280:
+masked_interrupt_book3e_0x2c0:
+	li	r11,PACA_HAPPENED_DBELL

arch/powerpc/kernel/exceptions-64e.S kernel_dbg_exc: · line 614

Quoted 6 lines

arch/powerpc/kernel/exceptions-64e.S +6 -0

+	b	masked_interrupt_book3e_no_mask
+
+masked_interrupt_book3e_no_mask:
+	mtcr	r10
+	lbz	r10,PACAIRQHAPPENED(r13)
+	ori	r10,r10,r11

Shouldn't this be an 'or'?

arch/powerpc/kernel/exceptions-64e.S kernel_dbg_exc: · line 620

Quoted 8 lines

arch/powerpc/kernel/exceptions-64e.S +5 -2

+	stb	r10,PACAIRQHAPPENED(r13)
+	b	1f
+masked_interrupt_book3e_full_mask:
  	mtcr	r10
-masked_interrupt_book3e_common:
-	stb	r11,PACAHARDIRQEN(r13)
+	lbz	r10,PACAIRQHAPPENED(r13)
+	ori	r10,r10,r11

Same comment.

Quoted 48 lines

arch/powerpc/kernel/exceptions-64e.S +33 -1

+	stb	r10,PACAIRQHAPPENED(r13)
  	mfspr	r10,SPRN_SRR1
  	rldicl	r11,r10,48,1		/* clear MSR_EE */
  	rotldi	r10,r11,16
  	mtspr	SPRN_SRR1,r10
-	ld	r10,PACA_EXGEN+EX_R10(r13);	/* restore registers */
+1:	ld	r10,PACA_EXGEN+EX_R10(r13);
  	ld	r11,PACA_EXGEN+EX_R11(r13);
  	mfspr	r13,SPRN_SPRG_GEN_SCRATCH;
  	rfi
  	b	.
 
  /*
+ * Called from arch_local_irq_enable when an interrupt needs
+ * to be resent. r3 contains either 0x500,0x900,0x260 or 0x280
+ * to indicate the kind of interrupt. MSR:EE is already off.
+ * We generate a stackframe like if a real interrupt had happened.
+ *
+ * Note: While MSR:EE is off, we need to make sure that _MSR
+ * in the generated frame has EE set to 1 or the exception
+ * handler will not properly re-enable them.
+ */
+_GLOBAL(__reemit_interrupt)
+	/* We are going to jump to the exception common code which
+	 * will retrieve various register values from the PACA which
+	 * we don't give a damn about.
+	 */
+	mflr	r10
+	mfmsr	r11
+	mfcr	r4;
+	mtspr	SPRN_SPRG_GEN_SCRATCH,r13;
+	std	r1,PACA_EXGEN+EX_R1(r13);
+	stw	r4,PACA_EXGEN+EX_CR(r13);
+	ori	r11,r11,MSR_EE
+	subi	r1,r1,INT_FRAME_SIZE;
+	cmpwi	cr0,r3,0x500
+	beq	exc_0x500_common
+	cmpwi	cr0,r3,0x900
+	beq+	exc_0x900_common
+	cmpwi	cr0,r3,0x280
+	beq+	exc_0x280_common
+	blr
+
+/*
   * This is called from 0x300 and 0x400 handlers after the prologs with
   * r14 and r15 containing the fault address and error code, with the
   * original values stashed away in the PACA

arch/powerpc/kernel/exceptions-64e.S BAD_STACK_TRAMPOLINE(0x000) · line 769

Quoted 8 lines

arch/powerpc/kernel/exceptions-64e.S +2 -0

@@ -680,6 +762,8 @@ BAD_STACK_TRAMPOLINE(0x000)
  BAD_STACK_TRAMPOLINE(0x100)
  BAD_STACK_TRAMPOLINE(0x200)
  BAD_STACK_TRAMPOLINE(0x260)
+BAD_STACK_TRAMPOLINE(0x280)
+BAD_STACK_TRAMPOLINE(0x2a0)
  BAD_STACK_TRAMPOLINE(0x2c0)
  BAD_STACK_TRAMPOLINE(0x2e0)
  BAD_STACK_TRAMPOLINE(0x300)

---
Best Regards, Laurentiu