Excerpts from Christophe Leroy's message of June 30, 2021 5:56 pm:

Le 30/06/2021 à 09:46, Nicholas Piggin a écrit :

quoted

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

Can we avoid that ifdef and use IS_ENABLED(CONFIG_PPC_BOOK3S_64) below ?

Hey Christophe,

Thanks for the review, sorry it was a bit rushed to get these fixes in
before the pull. I agree with this and there's a few other cleanups we
might do as well. Something to look at next.

quoted

  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

Allthough we are already in a PPC64 section, wouldn't it be better to use CONFIG_PPC_BOOK3S_64 ?

Can we use IS_ENABLED(CONFIG_PPC_BOOK3S_64) instead ?

Good question, it's a matter of preference. I have used PPC_BOOK3S in 
other places, but maybe in files shared by 32-bit it would be better to 
have the _64?

On the other hand, in cases where you have an else or #else, then you
still need the PPC64 context to understand that.

I don't really have a preference, I would go with either. Making some
convention and using it everywhere is probably a good idea though.

Thanks,
Nick