Re: [PATCH v3 3/9] powerpc/64e: remove implicit soft-masking and interrupt exit restart logic

The implicit soft-masking to speed up interrupt return was going to be
used by 64e as well, but it has not been extensively tested on that
platform and is not considered ready. It was intended to be disabled
before merge. Disable it for now.

Most of the restart code is common with 64s, so with more correctness
and performance testing this could be re-enabled again by adding the
extra soft-mask checks to interrupt handlers and flipping
exit_must_hard_disable().

Fixes: 9d1988ca87dd ("powerpc/64: treat low kernel text as irqs soft-masked")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
  arch/powerpc/include/asm/interrupt.h | 33 ++++++++++++++++++++--------
  arch/powerpc/kernel/exceptions-64e.S | 12 +---------
  arch/powerpc/kernel/interrupt.c      |  2 +-
  arch/powerpc/kernel/interrupt_64.S   | 16 ++++++++++++--
  4 files changed, 40 insertions(+), 23 deletions(-)

diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
index 8b4b1e84e110..f13c93b033c7 100644
--- a/arch/powerpc/include/asm/interrupt.h
+++ b/arch/powerpc/include/asm/interrupt.h

@@ -73,20 +73,34 @@
  #include <asm/kprobes.h>
  #include <asm/runlatch.h>
  
-#ifdef CONFIG_PPC64
+#ifdef CONFIG_PPC_BOOK3S_64

  extern char __end_soft_masked[];
  unsigned long search_kernel_restart_table(unsigned long addr);
-#endif
  
-#ifdef CONFIG_PPC_BOOK3S_64
  DECLARE_STATIC_KEY_FALSE(interrupt_exit_not_reentrant);
  
+static inline bool is_implicit_soft_masked(struct pt_regs *regs)
+{
+	if (regs->msr & MSR_PR)
+		return false;
+
+	if (regs->nip >= (unsigned long)__end_soft_masked)
+		return false;
+
+	return true;
+}
+
  static inline void srr_regs_clobbered(void)
  {
  	local_paca->srr_valid = 0;
  	local_paca->hsrr_valid = 0;
  }
  #else
+static inline bool is_implicit_soft_masked(struct pt_regs *regs)
+{
+	return false;
+}
+
  static inline void srr_regs_clobbered(void)
  {
  }

@@ -150,11 +164,13 @@ static inline void interrupt_enter_prepare(struct pt_regs *regs, struct interrup
  		 */
  		if (TRAP(regs) != INTERRUPT_PROGRAM) {
  			CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
-			BUG_ON(regs->nip < (unsigned long)__end_soft_masked);
+			BUG_ON(is_implicit_soft_masked(regs));
  		}
+#ifdef CONFIG_PPC_BOOK3S

  		/* Move this under a debugging check */
  		if (arch_irq_disabled_regs(regs))
  			BUG_ON(search_kernel_restart_table(regs->nip));
+#endif
  	}
  #endif
  

@@ -244,10 +260,9 @@ static inline void interrupt_nmi_enter_prepare(struct pt_regs *regs, struct inte
  	local_paca->irq_soft_mask = IRQS_ALL_DISABLED;
  	local_paca->irq_happened |= PACA_IRQ_HARD_DIS;
  
-	if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && !(regs->msr & MSR_PR) &&
-				regs->nip < (unsigned long)__end_soft_masked) {
-		// Kernel code running below __end_soft_masked is
-		// implicitly soft-masked.
+	if (is_implicit_soft_masked(regs)) {
+		// Adjust regs->softe soft implicit soft-mask, so
+		// arch_irq_disabled_regs(regs) behaves as expected.
  		regs->softe = IRQS_ALL_DISABLED;
  	}
  

@@ -282,6 +297,7 @@ static inline void interrupt_nmi_exit_prepare(struct pt_regs *regs, struct inter
  	 */
  
  #ifdef CONFIG_PPC64
+#ifdef CONFIG_PPC_BOOK3S

  	if (arch_irq_disabled_regs(regs)) {
  		unsigned long rst = search_kernel_restart_table(regs->nip);
  		if (rst)

@@ -289,7 +305,6 @@ static inline void interrupt_nmi_exit_prepare(struct pt_regs *regs, struct inter
  	}
  #endif
  
-#ifdef CONFIG_PPC64
  	if (nmi_disables_ftrace(regs))
  		this_cpu_set_ftrace_enabled(state->ftrace_enabled);
  

diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index d634bfceed2c..1401787b0b93 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S

@@ -342,17 +342,7 @@ ret_from_mc_except:
  #define PROLOG_ADDITION_MASKABLE_GEN(n)					    \
  	lbz	r10,PACAIRQSOFTMASK(r13);	/* are irqs soft-masked? */ \
  	andi.	r10,r10,IRQS_DISABLED;	/* yes -> go out of line */ \
-	bne	masked_interrupt_book3e_##n;				    \
-	/* Kernel code below __end_soft_masked is implicitly masked */	    \
-	andi.	r10,r11,MSR_PR;						    \
-	bne	1f;			/* user -> not masked */	    \
-	std	r14,PACA_EXGEN+EX_R14(r13);				    \
-	LOAD_REG_IMMEDIATE_SYM(r14, r10, __end_soft_masked);		    \
-	mfspr	r10,SPRN_SRR0;						    \
-	cmpld	r10,r14;						    \
-	ld	r14,PACA_EXGEN+EX_R14(r13);				    \
-	blt	masked_interrupt_book3e_##n;				    \
-1:
+	bne	masked_interrupt_book3e_##n
  
  /*
   * Additional regs must be re-loaded from paca before EXCEPTION_COMMON* is

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 0052702ee5ac..21bbd615ca41 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c

@@ -36,7 +36,7 @@ static inline bool exit_must_hard_disable(void)
  #else
  static inline bool exit_must_hard_disable(void)
  {
-	return IS_ENABLED(CONFIG_PPC32);
+	return true;
  }
  #endif
  

diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
index e7a50613a570..09b8d8846c67 100644
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S

@@ -231,7 +231,7 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_emulate)
  	li	r10,IRQS_ALL_DISABLED
  	stb	r10,PACAIRQSOFTMASK(r13)
  	b	system_call_vectored_common
-#endif
+#endif /* CONFIG_PPC_BOOK3S */
  
  	.balign IFETCH_ALIGN_BYTES
  	.globl system_call_common_real

@@ -320,10 +320,12 @@ END_BTB_FLUSH_SECTION
  	li	r5,0 /* !scv */
  	bl	syscall_exit_prepare
  	std	r1,PACA_EXIT_SAVE_R1(r13) /* save r1 for restart */
+#ifdef CONFIG_PPC_BOOK3S
  .Lsyscall_rst_start:
  	lbz	r11,PACAIRQHAPPENED(r13)
  	andi.	r11,r11,(~PACA_IRQ_HARD_DIS)@l
  	bne-	syscall_restart
+#endif
  	li	r11,IRQS_ENABLED
  	stb	r11,PACAIRQSOFTMASK(r13)
  	li	r11,0

@@ -396,6 +398,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
  	b	.Lsyscall_restore_regs_cont
  .Lsyscall_rst_end:
  
+#ifdef CONFIG_PPC_BOOK3S
  syscall_restart:
  	GET_PACA(r13)
  	ld	r1,PACA_EXIT_SAVE_R1(r13)

@@ -409,6 +412,7 @@ syscall_restart:
  	b	.Lsyscall_rst_start
  
  RESTART_TABLE(.Lsyscall_rst_start, .Lsyscall_rst_end, syscall_restart)
+#endif
  
  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
  tabort_syscall:

@@ -504,10 +508,12 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\())
  	bne-	.Lrestore_nvgprs_\srr
  .Lrestore_nvgprs_\srr\()_cont:
  	std	r1,PACA_EXIT_SAVE_R1(r13) /* save r1 for restart */
+#ifdef CONFIG_PPC_BOOK3S
  .Linterrupt_return_\srr\()_user_rst_start:
  	lbz	r11,PACAIRQHAPPENED(r13)
  	andi.	r11,r11,(~PACA_IRQ_HARD_DIS)@l
  	bne-	interrupt_return_\srr\()_user_restart
+#endif
  	li	r11,IRQS_ENABLED
  	stb	r11,PACAIRQSOFTMASK(r13)
  	li	r11,0

@@ -590,6 +596,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
  	REST_NVGPRS(r1)
  	b	.Lrestore_nvgprs_\srr\()_cont
  
+#ifdef CONFIG_PPC_BOOK3S
  interrupt_return_\srr\()_user_restart:
  	GET_PACA(r13)
  	ld	r1,PACA_EXIT_SAVE_R1(r13)

@@ -602,6 +609,7 @@ interrupt_return_\srr\()_user_restart:
  	b	.Linterrupt_return_\srr\()_user_rst_start
  
  RESTART_TABLE(.Linterrupt_return_\srr\()_user_rst_start, .Linterrupt_return_\srr\()_user_rst_end, interrupt_return_\srr\()_user_restart)
+#endif
  
  	.balign IFETCH_ALIGN_BYTES
  .Lkernel_interrupt_return_\srr\():

@@ -615,9 +623,11 @@ RESTART_TABLE(.Linterrupt_return_\srr\()_user_rst_start, .Linterrupt_return_\srr
  	cmpwi	r11,IRQS_ENABLED
  	stb	r11,PACAIRQSOFTMASK(r13)
  	bne	1f
+#ifdef CONFIG_PPC_BOOK3S
  	lbz	r11,PACAIRQHAPPENED(r13)
  	andi.	r11,r11,(~PACA_IRQ_HARD_DIS)@l
  	bne-	interrupt_return_\srr\()_kernel_restart
+#endif
  	li	r11,0
  	stb	r11,PACAIRQHAPPENED(r13) # clear out possible HARD_DIS
  1:

@@ -717,6 +727,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
  	b	.	/* prevent speculative execution */
  .Linterrupt_return_\srr\()_kernel_rst_end:
  
+#ifdef CONFIG_PPC_BOOK3S
  interrupt_return_\srr\()_kernel_restart:
  	GET_PACA(r13)
  	ld	r1,PACA_EXIT_SAVE_R1(r13)

@@ -729,14 +740,15 @@ interrupt_return_\srr\()_kernel_restart:
  	b	.Linterrupt_return_\srr\()_kernel_rst_start
  
  RESTART_TABLE(.Linterrupt_return_\srr\()_kernel_rst_start, .Linterrupt_return_\srr\()_kernel_rst_end, interrupt_return_\srr\()_kernel_restart)
+#endif
  
  .endm
  
  interrupt_return_macro srr
  #ifdef CONFIG_PPC_BOOK3S
  interrupt_return_macro hsrr
-#endif /* CONFIG_PPC_BOOK3S */
  
  	.globl __end_soft_masked
  __end_soft_masked:
  DEFINE_FIXED_SYMBOL(__end_soft_masked)
+#endif /* CONFIG_PPC_BOOK3S */