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

From: Leonardo Bras <[email-masked]>
Date: Tue, 21 Apr 2026 17:07:25 +0100

On Tue, Apr 21, 2026 at 08:58:57AM -0700, Breno Leitao wrote:
> 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 <[email-masked]>
> ---
> Changes in v2:
> - Expand the functions that uses always_inline in arm64
> - Link to v1: https://patch.msgid.link/[email-masked]
> ---
>  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 <[email-masked]>
> 

Looks correct to what was discussed in V1. FWIW:

Reviewed-by: Leonardo Bras <[email-masked]>