[PATCH 0/5] rework bad stack, sreset, hmi handling

[PATCH 0/5] rework bad stack, sreset, hmi handling

[Nicholas Piggin]

These are some significant changes to generated code here, again
with the aim of simplifying and improving code sharing.

Patches 1, 2-3, and 4-5 are independent in case any run into problems.

Last big thing to do is machine check I'll try to send out tonight.
After that we can start more unwinding of macros.

[ BTW, the end game here is that each handler should be able to more or
  less specify _what_ it wants to do in macro flags, and the generation
  that takes care of _how_ will mostly be in a single place. e.g.,
  Rather than some magic combination of EXCEPTION_<number>, it will just
  specify that it wants an early realmode handler with an alternate stack. ]

Nicholas Piggin (5):
  powerpc/64s/exception: remove bad stack branch
  powerpc/64s/exception: optimise system_reset for idle, clean up
    non-idle case
  powerpc/64s/exception: sreset move trampoline ahead of common code
  powerpc/64s/exception: hmi remove special case macro
  powerpc/64s/exception: simplify hmi control flow

 arch/powerpc/include/asm/exception-64s.h |   7 -
 arch/powerpc/include/asm/paca.h          |   2 +
 arch/powerpc/kernel/asm-offsets.c        |   2 +
 arch/powerpc/kernel/exceptions-64s.S     | 231 ++++++++---------------
 arch/powerpc/xmon/xmon.c                 |   2 +
 5 files changed, 86 insertions(+), 158 deletions(-)

-- 
2.20.1

[PATCH 1/5] powerpc/64s/exception: remove bad stack branch

[Nicholas Piggin]

The bad stack test in interrupt handlers has a few problems. For
performance it is taken in the common case, which is a fetch bubble
and a waste of i-cache.

For code development and maintainence, it requires yet another stack
frame setup routine, and that constrains all exception handlers to
follow the same register save pattern which inhibits future
optimisation.

Remove the test/branch and replace it with a trap. Teach the program
check handler to use the emergency stack for this case.

This does not result in quite so nice a message, however the SRR0 and
SRR1 of the crashed interrupt can be seen in r11 and r12, as is the
original r1 (adjusted by INT_FRAME_SIZE). These are the most important
parts to debugging the issue.

The original r9-12 and cr0 is lost, which is the main downside.

  kernel BUG at linux/arch/powerpc/kernel/exceptions-64s.S:847!
  Oops: Exception in kernel mode, sig: 5 [#1]
  BE SMP NR_CPUS=2048 NUMA PowerNV
  Modules linked in:
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted
  NIP:  c000000000009108 LR: c000000000cadbcc CTR: c0000000000090f0
  REGS: c0000000fffcbd70 TRAP: 0700   Not tainted
  MSR:  9000000000021032 <SF,HV,ME,IR,DR,RI>  CR: 28222448  XER: 20040000
  CFAR: c000000000009100 IRQMASK: 0
  GPR00: 000000000000003d fffffffffffffd00 c0000000018cfb00 c0000000f02b3166
  GPR04: fffffffffffffffd 0000000000000007 fffffffffffffffb 0000000000000030
  GPR08: 0000000000000037 0000000028222448 0000000000000000 c000000000ca8de0
  GPR12: 9000000002009032 c000000001ae0000 c000000000010a00 0000000000000000
  GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR20: c0000000f00322c0 c000000000f85200 0000000000000004 ffffffffffffffff
  GPR24: fffffffffffffffe 0000000000000000 0000000000000000 000000000000000a
  GPR28: 0000000000000000 0000000000000000 c0000000f02b391c c0000000f02b3167
  NIP [c000000000009108] decrementer_common+0x18/0x160
  LR [c000000000cadbcc] .vsnprintf+0x3ec/0x4f0
  Call Trace:
  Instruction dump:
  996d098a 994d098b 38610070 480246ed 48005518 60000000 38200000 718a4000
  7c2a0b78 3821fd00 41c20008 e82d0970 <0981fd00> f92101a0 f9610170 f9810178

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/include/asm/exception-64s.h |  7 --
 arch/powerpc/include/asm/paca.h          |  2 +
 arch/powerpc/kernel/asm-offsets.c        |  2 +
 arch/powerpc/kernel/exceptions-64s.S     | 96 ++++--------------------
 arch/powerpc/xmon/xmon.c                 |  2 +
 5 files changed, 22 insertions(+), 87 deletions(-)

diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 2e919253a075..33f4f72eb035 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -44,13 +44,6 @@
  */
 #define MAX_MCE_DEPTH	4
 
-/*
- * EX_R3 is only used by the bad_stack handler. bad_stack reloads and
- * saves DAR from SPRN_DAR, and EX_DAR is not used. So EX_R3 can overlap
- * with EX_DAR.
- */
-#define EX_R3		EX_DAR
-
 #ifdef __ASSEMBLY__
 
 #define STF_ENTRY_BARRIER_SLOT						\
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 9bd2326bef6f..e3cc9eb9204d 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -166,7 +166,9 @@ struct paca_struct {
 	u64 kstack;			/* Saved Kernel stack addr */
 	u64 saved_r1;			/* r1 save for RTAS calls or PM or EE=0 */
 	u64 saved_msr;			/* MSR saved here by enter_rtas */
+#ifdef CONFIG_PPC_BOOK3E
 	u16 trap_save;			/* Used when bad stack is encountered */
+#endif
 	u8 irq_soft_mask;		/* mask for irq soft masking */
 	u8 irq_happened;		/* irq happened while soft-disabled */
 	u8 irq_work_pending;		/* IRQ_WORK interrupt while soft-disable */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 31dc7e64cbfc..4ccb6b3a7fbd 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -266,7 +266,9 @@ int main(void)
 	OFFSET(ACCOUNT_STARTTIME_USER, paca_struct, accounting.starttime_user);
 	OFFSET(ACCOUNT_USER_TIME, paca_struct, accounting.utime);
 	OFFSET(ACCOUNT_SYSTEM_TIME, paca_struct, accounting.stime);
+#ifdef CONFIG_PPC_BOOK3E
 	OFFSET(PACA_TRAP_SAVE, paca_struct, trap_save);
+#endif
 	OFFSET(PACA_SPRG_VDSO, paca_struct, sprg_vdso);
 #else /* CONFIG_PPC64 */
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 0857c696480c..9aafe86193db 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -411,14 +411,8 @@ END_FTR_SECTION_NESTED(CPU_FTR_CFAR, CPU_FTR_CFAR, 66);			   \
 	subi	r1,r1,INT_FRAME_SIZE;	/* alloc frame on kernel stack	*/ \
 	beq-	1f;							   \
 	ld	r1,PACAKSAVE(r13);	/* kernel stack to use		*/ \
-1:	cmpdi	cr1,r1,-INT_FRAME_SIZE;	/* check if r1 is in userspace	*/ \
-	blt+	cr1,3f;			/* abort if it is		*/ \
-	li	r1,(trap);		/* will be reloaded later	*/ \
-	sth	r1,PACA_TRAP_SAVE(r13);					   \
-	std	r3,area+EX_R3(r13);					   \
-	addi	r3,r13,area;		/* r3 -> where regs are saved*/	   \
-	RESTORE_CTR(r1, area);						   \
-	b	bad_stack;						   \
+1:	tdgei	r1,-INT_FRAME_SIZE;	/* trap if r1 is in userspace	*/ \
+	EMIT_BUG_ENTRY 1b,__FILE__,__LINE__,0;				   \
 3:	EXCEPTION_PROLOG_COMMON_1();					   \
 	kuap_save_amr_and_lock r9, r10, cr1, cr0;			   \
 	beq	4f;			/* if from kernel mode		*/ \
@@ -428,7 +422,6 @@ END_FTR_SECTION_NESTED(CPU_FTR_CFAR, CPU_FTR_CFAR, 66);			   \
 	EXCEPTION_PROLOG_COMMON_3(trap);				   \
 	ACCOUNT_STOLEN_TIME
 
-
 /*
  * Exception where stack is already set in r1, r1 is saved in r10.
  * PPR save and CPU accounting is not done (for some reason).
@@ -1453,21 +1446,25 @@ EXC_COMMON_BEGIN(program_check_common)
 	 * we switch to the emergency stack if we're taking a TM Bad Thing from
 	 * the kernel.
 	 */
-	li	r10,MSR_PR		/* Build a mask of MSR_PR ..	*/
-	oris	r10,r10,0x200000@h	/* .. and SRR1_PROGTM		*/
-	and	r10,r10,r12		/* Mask SRR1 with that.		*/
-	srdi	r10,r10,8		/* Shift it so we can compare	*/
-	cmpldi	r10,(0x200000 >> 8)	/* .. with an immediate.	*/
-	bne 1f				/* If != go to normal path.	*/
-
-	/* SRR1 had PR=0 and SRR1_PROGTM=1, so use the emergency stack	*/
-	andi.	r10,r12,MSR_PR;		/* Set CR0 correctly for label	*/
+
+	andi.	r10,r12,MSR_PR
+	bne	2f			/* If userspace, go normal path */
+
+	andis.	r10,r12,(SRR1_PROGTM)@h
+	bne	1f			/* If TM, emergency		*/
+
+	cmpdi	r1,-INT_FRAME_SIZE	/* check if r1 is in userspace	*/
+	blt	2f			/* normal path if not		*/
+
+	/* Use the emergency stack					*/
+1:	andi.	r10,r12,MSR_PR		/* Set CR0 correctly for label	*/
 					/* 3 in EXCEPTION_PROLOG_COMMON	*/
 	mr	r10,r1			/* Save r1			*/
 	ld	r1,PACAEMERGSP(r13)	/* Use emergency stack		*/
 	subi	r1,r1,INT_FRAME_SIZE	/* alloc stack frame		*/
 	b 3f				/* Jump into the macro !!	*/
-1:	EXCEPTION_COMMON(PACA_EXGEN, 0x700)
+2:
+	EXCEPTION_COMMON(PACA_EXGEN, 0x700)
 	bl	save_nvgprs
 	RECONCILE_IRQ_STATE(r10, r11)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
@@ -2403,67 +2400,6 @@ handle_dabr_fault:
 	bl	bad_page_fault
 	b	ret_from_except
 
-/*
- * Here we have detected that the kernel stack pointer is bad.
- * R9 contains the saved CR, r13 points to the paca,
- * r10 contains the (bad) kernel stack pointer,
- * r11 and r12 contain the saved SRR0 and SRR1.
- * We switch to using an emergency stack, save the registers there,
- * and call kernel_bad_stack(), which panics.
- */
-bad_stack:
-	ld	r1,PACAEMERGSP(r13)
-	subi	r1,r1,64+INT_FRAME_SIZE
-	std	r9,_CCR(r1)
-	std	r10,GPR1(r1)
-	std	r11,_NIP(r1)
-	std	r12,_MSR(r1)
-	mfspr	r11,SPRN_DAR
-	mfspr	r12,SPRN_DSISR
-	std	r11,_DAR(r1)
-	std	r12,_DSISR(r1)
-	mflr	r10
-	mfctr	r11
-	mfxer	r12
-	std	r10,_LINK(r1)
-	std	r11,_CTR(r1)
-	std	r12,_XER(r1)
-	SAVE_GPR(0,r1)
-	SAVE_GPR(2,r1)
-	ld	r10,EX_R3(r3)
-	std	r10,GPR3(r1)
-	SAVE_GPR(4,r1)
-	SAVE_4GPRS(5,r1)
-	ld	r9,EX_R9(r3)
-	ld	r10,EX_R10(r3)
-	SAVE_2GPRS(9,r1)
-	ld	r9,EX_R11(r3)
-	ld	r10,EX_R12(r3)
-	ld	r11,EX_R13(r3)
-	std	r9,GPR11(r1)
-	std	r10,GPR12(r1)
-	std	r11,GPR13(r1)
-BEGIN_FTR_SECTION
-	ld	r10,EX_CFAR(r3)
-	std	r10,ORIG_GPR3(r1)
-END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
-	SAVE_8GPRS(14,r1)
-	SAVE_10GPRS(22,r1)
-	lhz	r12,PACA_TRAP_SAVE(r13)
-	std	r12,_TRAP(r1)
-	addi	r11,r1,INT_FRAME_SIZE
-	std	r11,0(r1)
-	li	r12,0
-	std	r12,0(r11)
-	ld	r2,PACATOC(r13)
-	ld	r11,exception_marker@toc(r2)
-	std	r12,RESULT(r1)
-	std	r11,STACK_FRAME_OVERHEAD-16(r1)
-1:	addi	r3,r1,STACK_FRAME_OVERHEAD
-	bl	kernel_bad_stack
-	b	1b
-_ASM_NOKPROBE_SYMBOL(bad_stack);
-
 /*
  * When doorbell is triggered from system reset wakeup, the message is
  * not cleared, so it would fire again when EE is enabled.
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index d0620d762a5a..41c91f17e408 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -2448,7 +2448,9 @@ static void dump_one_paca(int cpu)
 	DUMP(p, canary, "%#-*lx");
 #endif
 	DUMP(p, saved_r1, "%#-*llx");
+#ifdef CONFIG_PPC_BOOK3E
 	DUMP(p, trap_save, "%#-*x");
+#endif
 	DUMP(p, irq_soft_mask, "%#-*x");
 	DUMP(p, irq_happened, "%#-*x");
 #ifdef CONFIG_MMIOWB
-- 
2.20.1

[PATCH 2/5] powerpc/64s/exception: optimise system_reset for idle, clean up non-idle case

[Nicholas Piggin]

The idle wake up code in the system reset interrupt is not very
optimal. There are two requirements: perform idle wake up quickly;
and save everything including CFAR for non-idle interrupts, with
no performance requirement.

The problem with placing the idle test in the middle of the handler
and using the normal handler code to save CFAR, is that it's quite
costly (e.g., mfcfar is serialising, speculative workarounds get
applied, SRR1 has to be reloaded, etc). It also prevents the standard
interrupt handler boilerplate being used.

This pain can be avoided by using a dedicated idle interrupt handler
at the start of the interrupt handler, which restores all registers
back to the way they were in case it was not an idle wake up. CFAR
is preserved without saving it before the non-idle case by making that
the fall-through, and idle is a taken branch.

Performance seems to be in the noise, but possibly around 0.5% faster,
the executed instructions certainly look better. The bigger benefit is
being able to drop in standard interrupt handlers after the idle code,
which helps with subsequent cleanup and consolidation.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S | 69 +++++++++++++++-------------
 1 file changed, 38 insertions(+), 31 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 9aafe86193db..4b33aadd142c 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -256,7 +256,7 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
  * load KBASE for a slight optimisation.
  */
 #define BRANCH_TO_C000(reg, label)					\
-	__LOAD_HANDLER(reg, label);					\
+	__LOAD_FAR_HANDLER(reg, label);					\
 	mtctr	reg;							\
 	bctr
 
@@ -822,15 +822,6 @@ EXC_VIRT_NONE(0x4000, 0x100)
 
 
 EXC_REAL_BEGIN(system_reset, 0x100, 0x100)
-	EXCEPTION_PROLOG_0 PACA_EXNMI
-
-	/* This is EXCEPTION_PROLOG_1 with the idle feature section added */
-	OPT_SAVE_REG_TO_PACA(PACA_EXNMI+EX_PPR, r9, CPU_FTR_HAS_PPR)
-	OPT_SAVE_REG_TO_PACA(PACA_EXNMI+EX_CFAR, r10, CPU_FTR_CFAR)
-	INTERRUPT_TO_KERNEL
-	SAVE_CTR(r10, PACA_EXNMI)
-	mfcr	r9
-
 #ifdef CONFIG_PPC_P7_NAP
 	/*
 	 * If running native on arch 2.06 or later, check if we are waking up
@@ -838,43 +829,59 @@ EXC_REAL_BEGIN(system_reset, 0x100, 0x100)
 	 * bits 46:47. A non-0 value indicates that we are coming from a power
 	 * saving state. The idle wakeup handler initially runs in real mode,
 	 * but we branch to the 0xc000... address so we can turn on relocation
-	 * with mtmsr.
+	 * with mtmsrd later, after SPRs are restored.
+	 *
+	 * Careful to minimise cost for the fast path (idle wakeup) while
+	 * also avoiding clobbering CFAR for the debug path (non-idle).
+	 *
+	 * For the idle wake case volatile registers can be clobbered, which
+	 * is why we use those initially. If it turns out to not be an idle
+	 * wake, carefully put everything back the way it was, so we can use
+	 * common exception macros to handle it.
 	 */
 BEGIN_FTR_SECTION
-	mfspr	r10,SPRN_SRR1
-	rlwinm.	r10,r10,47-31,30,31
-	beq-	1f
-	cmpwi	cr1,r10,2
+	SET_SCRATCH0(r13)
+	GET_PACA(r13)
+	std	r3,PACA_EXNMI+0*8(r13)
+	std	r4,PACA_EXNMI+1*8(r13)
+	std	r5,PACA_EXNMI+2*8(r13)
 	mfspr	r3,SPRN_SRR1
-	bltlr	cr1	/* no state loss, return to idle caller */
-	BRANCH_TO_C000(r10, system_reset_idle_common)
-1:
+	mfocrf	r4,0x80
+	rlwinm.	r5,r3,47-31,30,31
+	bne+	system_reset_idle_wake
+	/* Not powersave wakeup. Restore regs for regular interrupt handler. */
+	mtocrf	0x80,r4
+	ld	r3,PACA_EXNMI+0*8(r13)
+	ld	r4,PACA_EXNMI+1*8(r13)
+	ld	r5,PACA_EXNMI+2*8(r13)
+	GET_SCRATCH0(r13)
 END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
 #endif
 
-	KVMTEST EXC_STD 0x100
-	std	r11,PACA_EXNMI+EX_R11(r13)
-	std	r12,PACA_EXNMI+EX_R12(r13)
-	GET_SCRATCH0(r10)
-	std	r10,PACA_EXNMI+EX_R13(r13)
-
+	EXCEPTION_PROLOG_0 PACA_EXNMI
+	EXCEPTION_PROLOG_1 EXC_STD, PACA_EXNMI, 1, 0x100, 0, 0, 0
 	EXCEPTION_PROLOG_2_REAL system_reset_common, EXC_STD, 0
 	/*
 	 * MSR_RI is not enabled, because PACA_EXNMI and nmi stack is
 	 * being used, so a nested NMI exception would corrupt it.
+	 *
+	 * In theory, we should not enable relocation here if it was disabled
+	 * in SRR1, because the MMU may not be configured to support it (e.g.,
+	 * SLB may have been cleared). In practice, there should only be a few
+	 * small windows where that's the case, and sreset is considered to
+	 * be dangerous anyway.
 	 */
-
 EXC_REAL_END(system_reset, 0x100, 0x100)
+
 EXC_VIRT_NONE(0x4100, 0x100)
 TRAMP_KVM(PACA_EXNMI, 0x100)
 
 #ifdef CONFIG_PPC_P7_NAP
-EXC_COMMON_BEGIN(system_reset_idle_common)
-	/*
-	 * This must be a direct branch (without linker branch stub) because
-	 * we can not use TOC at this point as r2 may not be restored yet.
-	 */
-	b	idle_return_gpr_loss
+TRAMP_REAL_BEGIN(system_reset_idle_wake)
+	/* We are waking up from idle, so may clobber any volatile register */
+	cmpwi	cr1,r5,2
+	bltlr	cr1	/* no state loss, return to idle caller with r3=SRR1 */
+	BRANCH_TO_C000(r12, idle_return_gpr_loss)
 #endif
 
 EXC_COMMON_BEGIN(system_reset_common)
-- 
2.20.1

[PATCH 3/5] powerpc/64s/exception: sreset move trampoline ahead of common code

[Nicholas Piggin]

Follow convention and move tramp ahead of common.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 4b33aadd142c..89ea4f3b07cb 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -884,6 +884,18 @@ TRAMP_REAL_BEGIN(system_reset_idle_wake)
 	BRANCH_TO_C000(r12, idle_return_gpr_loss)
 #endif
 
+#ifdef CONFIG_PPC_PSERIES
+/*
+ * Vectors for the FWNMI option.  Share common code.
+ */
+TRAMP_REAL_BEGIN(system_reset_fwnmi)
+	/* See comment at system_reset exception, don't turn on RI */
+	EXCEPTION_PROLOG_0 PACA_EXNMI
+	EXCEPTION_PROLOG_1 EXC_STD, PACA_EXNMI, 0, 0x100, 0, 0, 0
+	EXCEPTION_PROLOG_2_REAL system_reset_common, EXC_STD, 0
+
+#endif /* CONFIG_PPC_PSERIES */
+
 EXC_COMMON_BEGIN(system_reset_common)
 	/*
 	 * Increment paca->in_nmi then enable MSR_RI. SLB or MCE will be able
@@ -941,18 +953,6 @@ EXC_COMMON_BEGIN(system_reset_common)
 	EXCEPTION_RESTORE_REGS EXC_STD
 	RFI_TO_USER_OR_KERNEL
 
-#ifdef CONFIG_PPC_PSERIES
-/*
- * Vectors for the FWNMI option.  Share common code.
- */
-TRAMP_REAL_BEGIN(system_reset_fwnmi)
-	/* See comment at system_reset exception, don't turn on RI */
-	EXCEPTION_PROLOG_0 PACA_EXNMI
-	EXCEPTION_PROLOG_1 EXC_STD, PACA_EXNMI, 0, 0x100, 0, 0, 0
-	EXCEPTION_PROLOG_2_REAL system_reset_common, EXC_STD, 0
-
-#endif /* CONFIG_PPC_PSERIES */
-
 
 EXC_REAL_BEGIN(machine_check, 0x200, 0x100)
 	/* This is moved out of line as it can be patched by FW, but
-- 
2.20.1

[PATCH 4/5] powerpc/64s/exception: hmi remove special case macro

[Nicholas Piggin]

No code change.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 89ea4f3b07cb..23aba27b2f59 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -519,11 +519,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
  *
  * There can be combinations, e.g., EXC_VIRT_OOL_MASKABLE_HV
  *
- * The one unusual case is __EXC_REAL_OOL_HV_DIRECT, which is
- * an OOL vector that branches to a specified handler rather than the usual
- * trampoline that goes to common. It, and other underscore macros, should
- * be used with care.
- *
  * KVM handlers come in the following verieties:
  * TRAMP_KVM
  * TRAMP_KVM_SKIP
@@ -614,12 +609,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
 	__EXC_REAL_OOL_MASKABLE(name, start, size);			\
 	__TRAMP_REAL_OOL_MASKABLE(name, start, bitmask)
 
-#define __EXC_REAL_OOL_HV_DIRECT(name, start, size, handler)		\
-	EXC_REAL_BEGIN(name, start, size);				\
-	EXCEPTION_PROLOG_0 PACA_EXGEN ;					\
-	b	handler;						\
-	EXC_REAL_END(name, start, size)
-
 #define __EXC_REAL_OOL_HV(name, start, size)				\
 	__EXC_REAL_OOL(name, start, size)
 
@@ -1720,7 +1709,10 @@ EXC_COMMON(emulation_assist_common, 0xe40, emulation_assist_interrupt)
  * first, and then eventaully from there to the trampoline to get into virtual
  * mode.
  */
-__EXC_REAL_OOL_HV_DIRECT(hmi_exception, 0xe60, 0x20, hmi_exception_early)
+EXC_REAL_BEGIN(hmi_exception, 0xe60, 0x20)
+	EXCEPTION_PROLOG_0 PACA_EXGEN
+	b	hmi_exception_early
+EXC_REAL_END(hmi_exception, 0xe60, 0x20)
 __TRAMP_REAL_OOL_MASKABLE_HV(hmi_exception, 0xe60, IRQS_DISABLED)
 EXC_VIRT_NONE(0x4e60, 0x20)
 TRAMP_KVM_HV(PACA_EXGEN, 0xe60)
-- 
2.20.1

[PATCH 5/5] powerpc/64s/exception: simplify hmi control flow

[Nicholas Piggin]

Branch to the relocated 0xc000 address early (still in real mode), to
simplify subsequent branches. Have the virt mode handler avoid just
'windup' and redo the exception from scratch, rather than branching
back to the trampoline.

Rearrange the stack setup instruction location to match the system
reset handler (e.g., right before EXCEPTION_PROLOG_COMMON).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 23aba27b2f59..a91541956aa0 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -260,17 +260,6 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 	mtctr	reg;							\
 	bctr
 
-#ifdef CONFIG_RELOCATABLE
-#define BRANCH_LINK_TO_FAR(label)					\
-	__LOAD_FAR_HANDLER(r12, label);					\
-	mtctr	r12;							\
-	bctrl
-
-#else
-#define BRANCH_LINK_TO_FAR(label)					\
-	bl	label
-#endif
-
 #ifdef CONFIG_KVM_BOOK3S_64_HANDLER
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 /*
@@ -1713,22 +1702,26 @@ EXC_REAL_BEGIN(hmi_exception, 0xe60, 0x20)
 	EXCEPTION_PROLOG_0 PACA_EXGEN
 	b	hmi_exception_early
 EXC_REAL_END(hmi_exception, 0xe60, 0x20)
-__TRAMP_REAL_OOL_MASKABLE_HV(hmi_exception, 0xe60, IRQS_DISABLED)
 EXC_VIRT_NONE(0x4e60, 0x20)
 TRAMP_KVM_HV(PACA_EXGEN, 0xe60)
 TRAMP_REAL_BEGIN(hmi_exception_early)
 	EXCEPTION_PROLOG_1 EXC_HV, PACA_EXGEN, 1, 0xe60, 0, 0, 0
+	mfctr	r10			/* save ctr, even for !RELOCATABLE */
+	BRANCH_TO_C000(r11, hmi_exception_early_common)
+
+EXC_COMMON_BEGIN(hmi_exception_early_common)
+	mtctr	r10			/* Restore ctr */
+	mfspr	r11,SPRN_HSRR0		/* Save HSRR0 */
+	mfspr	r12,SPRN_HSRR1		/* Save HSRR1 */
 	mr	r10,r1			/* Save r1 */
 	ld	r1,PACAEMERGSP(r13)	/* Use emergency stack for realmode */
 	subi	r1,r1,INT_FRAME_SIZE	/* alloc stack frame		*/
-	mfspr	r11,SPRN_HSRR0		/* Save HSRR0 */
-	mfspr	r12,SPRN_HSRR1		/* Save HSRR1 */
 	EXCEPTION_PROLOG_COMMON_1()
 	/* We don't touch AMR here, we never go to virtual mode */
 	EXCEPTION_PROLOG_COMMON_2(PACA_EXGEN)
 	EXCEPTION_PROLOG_COMMON_3(0xe60)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	BRANCH_LINK_TO_FAR(DOTSYM(hmi_exception_realmode)) /* Function call ABI */
+	bl	hmi_exception_realmode
 	cmpdi	cr0,r3,0
 	bne	1f
 
@@ -1742,7 +1735,8 @@ TRAMP_REAL_BEGIN(hmi_exception_early)
 	 */
 	EXCEPTION_RESTORE_REGS EXC_HV
 	EXCEPTION_PROLOG_0 PACA_EXGEN
-	b	tramp_real_hmi_exception
+	EXCEPTION_PROLOG_1 EXC_HV, PACA_EXGEN, 1, 0xe60, 0, 0, IRQS_DISABLED
+	EXCEPTION_PROLOG_2_REAL hmi_exception_common, EXC_HV, 1
 
 EXC_COMMON_BEGIN(hmi_exception_common)
 	EXCEPTION_COMMON(PACA_EXGEN, 0xe60)
-- 
2.20.1

Re: [PATCH 1/5] powerpc/64s/exception: remove bad stack branch

[Michael Ellerman]

On Fri, 2019-06-28 at 06:33:18 UTC, Nicholas Piggin wrote:
> The bad stack test in interrupt handlers has a few problems. For
> performance it is taken in the common case, which is a fetch bubble
> and a waste of i-cache.
> 
> For code development and maintainence, it requires yet another stack
> frame setup routine, and that constrains all exception handlers to
> follow the same register save pattern which inhibits future
> optimisation.
> 
> Remove the test/branch and replace it with a trap. Teach the program
> check handler to use the emergency stack for this case.
> 
> This does not result in quite so nice a message, however the SRR0 and
> SRR1 of the crashed interrupt can be seen in r11 and r12, as is the
> original r1 (adjusted by INT_FRAME_SIZE). These are the most important
> parts to debugging the issue.
> 
> The original r9-12 and cr0 is lost, which is the main downside.
> 
>   kernel BUG at linux/arch/powerpc/kernel/exceptions-64s.S:847!
>   Oops: Exception in kernel mode, sig: 5 [#1]
>   BE SMP NR_CPUS=2048 NUMA PowerNV
>   Modules linked in:
>   CPU: 0 PID: 1 Comm: swapper/0 Not tainted
>   NIP:  c000000000009108 LR: c000000000cadbcc CTR: c0000000000090f0
>   REGS: c0000000fffcbd70 TRAP: 0700   Not tainted
>   MSR:  9000000000021032 <SF,HV,ME,IR,DR,RI>  CR: 28222448  XER: 20040000
>   CFAR: c000000000009100 IRQMASK: 0
>   GPR00: 000000000000003d fffffffffffffd00 c0000000018cfb00 c0000000f02b3166
>   GPR04: fffffffffffffffd 0000000000000007 fffffffffffffffb 0000000000000030
>   GPR08: 0000000000000037 0000000028222448 0000000000000000 c000000000ca8de0
>   GPR12: 9000000002009032 c000000001ae0000 c000000000010a00 0000000000000000
>   GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR20: c0000000f00322c0 c000000000f85200 0000000000000004 ffffffffffffffff
>   GPR24: fffffffffffffffe 0000000000000000 0000000000000000 000000000000000a
>   GPR28: 0000000000000000 0000000000000000 c0000000f02b391c c0000000f02b3167
>   NIP [c000000000009108] decrementer_common+0x18/0x160
>   LR [c000000000cadbcc] .vsnprintf+0x3ec/0x4f0
>   Call Trace:
>   Instruction dump:
>   996d098a 994d098b 38610070 480246ed 48005518 60000000 38200000 718a4000
>   7c2a0b78 3821fd00 41c20008 e82d0970 <0981fd00> f92101a0 f9610170 f9810178
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/0a882e28468f48ab3d9a36dde0a5723ea29ed1ed

cheers