[PATCH v2] arm64/irqflags: __always_inline the arch_local_irq_*() helpers

[Breno Leitao <leitao@debian.org>]

The arch_local_irq_*() wrappers in <asm/irqflags.h> dispatch between two
underlying primitives: the __daif_* path on most systems, and the
__pmr_* path on builds that use GIC PMR-based masking (Pseudo-NMI). The
leaf primitives are already __always_inline, but the wrappers themselves
are plain "static inline".

That is unsafe for noinstr callers: nothing prevents the compiler from
emitting an out-of-line copy of e.g. arch_local_irq_disable(), and an
out-of-line copy can be instrumented (ftrace, kcov, sanitizers), which
breaks the noinstr contract on the entry/idle paths that rely on these
helpers.

x86 hit and fixed exactly this class of bug in commit 7a745be1cc90
("x86/entry: __always_inline irqflags for noinstr").

Force-inline all of the arch_local_irq_*() wrappers so they cannot be
emitted out-of-line:

  - arch_local_irq_enable()
  - arch_local_irq_disable()
  - arch_local_save_flags()
  - arch_irqs_disabled_flags()
  - arch_irqs_disabled()
  - arch_local_irq_save()
  - arch_local_irq_restore()

The primary motivation is noinstr safety. There is a useful side effect
for fleet-wide profiling: when the wrapper is emitted out-of-line,
samples taken inside it during the post-WFI IRQ unmask in
default_idle_call() are attributed to arch_local_irq_enable rather than
default_idle_call(), and the FP-unwinder loses default_idle_call() from
the chain.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Changes in v2:
- Expand the functions that uses always_inline in arm64
- Link to v1: https://patch.msgid.link/20260420-arm64_always_inline-v1-1-dba919cf46bc@debian.org
---
 arch/arm64/include/asm/irqflags.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
index d4d7451c2c129..a8cb5a5c93b78 100644
--- a/arch/arm64/include/asm/irqflags.h
+++ b/arch/arm64/include/asm/irqflags.h
@@ -40,7 +40,7 @@ static __always_inline void __pmr_local_irq_enable(void)
 	barrier();
 }
 
-static inline void arch_local_irq_enable(void)
+static __always_inline void arch_local_irq_enable(void)
 {
 	if (system_uses_irq_prio_masking()) {
 		__pmr_local_irq_enable();
@@ -68,7 +68,7 @@ static __always_inline void __pmr_local_irq_disable(void)
 	barrier();
 }
 
-static inline void arch_local_irq_disable(void)
+static __always_inline void arch_local_irq_disable(void)
 {
 	if (system_uses_irq_prio_masking()) {
 		__pmr_local_irq_disable();
@@ -90,7 +90,7 @@ static __always_inline unsigned long __pmr_local_save_flags(void)
 /*
  * Save the current interrupt enable state.
  */
-static inline unsigned long arch_local_save_flags(void)
+static __always_inline unsigned long arch_local_save_flags(void)
 {
 	if (system_uses_irq_prio_masking()) {
 		return __pmr_local_save_flags();
@@ -109,7 +109,7 @@ static __always_inline bool __pmr_irqs_disabled_flags(unsigned long flags)
 	return flags != GIC_PRIO_IRQON;
 }
 
-static inline bool arch_irqs_disabled_flags(unsigned long flags)
+static __always_inline bool arch_irqs_disabled_flags(unsigned long flags)
 {
 	if (system_uses_irq_prio_masking()) {
 		return __pmr_irqs_disabled_flags(flags);
@@ -128,7 +128,7 @@ static __always_inline bool __pmr_irqs_disabled(void)
 	return __pmr_irqs_disabled_flags(__pmr_local_save_flags());
 }
 
-static inline bool arch_irqs_disabled(void)
+static __always_inline bool arch_irqs_disabled(void)
 {
 	if (system_uses_irq_prio_masking()) {
 		return __pmr_irqs_disabled();
@@ -160,7 +160,7 @@ static __always_inline unsigned long __pmr_local_irq_save(void)
 	return flags;
 }
 
-static inline unsigned long arch_local_irq_save(void)
+static __always_inline unsigned long arch_local_irq_save(void)
 {
 	if (system_uses_irq_prio_masking()) {
 		return __pmr_local_irq_save();
@@ -187,7 +187,7 @@ static __always_inline void __pmr_local_irq_restore(unsigned long flags)
 /*
  * restore saved IRQ state
  */
-static inline void arch_local_irq_restore(unsigned long flags)
+static __always_inline void arch_local_irq_restore(unsigned long flags)
 {
 	if (system_uses_irq_prio_masking()) {
 		__pmr_local_irq_restore(flags);

---
base-commit: bee6ea30c48788e18348309f891ed8afbf7702ac
change-id: 20260420-arm64_always_inline-6bc9dd3c17e6

Best regards,
--  
Breno Leitao <leitao@debian.org>