On Fri, Sep 04, 2026 at 02:38:58PM +0530, Mukesh Kumar Chaurasiya (IBM) wrote:
> When __replay_soft_interrupts() replays a pending interrupt (e.g.
> PACA_IRQ_DEC -> timer_interrupt), it calls the handler directly with a
> synthetic pt_regs. The DEFINE_INTERRUPT_HANDLER_ASYNC wrapper around
> each handler calls arch_interrupt_async_exit_prepare() on the way out,
> which calls arch_interrupt_exit_prepare() -> local_irq_disable() ->
> arch_local_irq_disable(), which does:
>
> irq_soft_mask_set(IRQS_DISABLED) /* 0x1 */
>
> This unconditionally overwrites irq_soft_mask with IRQS_DISABLED (0x1),
> stripping the IRQS_PMI_DISABLED (0x2) bit. The result is that
> irq_soft_mask is 0x1 instead of IRQS_ALL_DISABLED (0x3) when the
> handler returns to __replay_soft_interrupts().
>
> For a normally-taken interrupt this is harmless: the next interrupt
> always enters through arch_interrupt_enter_prepare() which
> unconditionally sets irq_soft_mask to IRQS_ALL_DISABLED. But during
> replay, next_interrupt() is called directly between replayed handlers
> without going back through arch_interrupt_enter_prepare(), so the
> stripped bit is never restored. next_interrupt() then fires a WARNING:
>
> WARNING: arch/powerpc/kernel/irq_64.c:75
> WARN_ON(irq_soft_mask_return() != IRQS_ALL_DISABLED)
>
> The warning was observed early in boot on a POWER10 pseries guest
> during kmem_cache_init_late(), where a spinlock release triggers
> interrupt replay that processes a pending timer interrupt.
>
> Debugger state confirming the bug:
> Before timer_interrupt(®s):
> irq_soft_mask = 0x3 (IRQS_ALL_DISABLED) correct
> irq_happened = 0x41 (HARD_DIS|REPLAYING) correct
> After timer_interrupt(®s) returns:
> irq_soft_mask = 0x1 (IRQS_DISABLED) WRONG - PMI bit stripped
> irq_happened = 0x41 unchanged
>
> The fix is to replace local_irq_disable() with hard_irq_disable().
>
> hard_irq_disable() is the right primitive here for two reasons:
>
> 1. On PPC64 (hw_irq.h:301) it calls
> irq_soft_mask_set_return(IRQS_ALL_DISABLED),
> setting the soft mask to 0x3 (both IRQS_DISABLED and IRQS_PMI_DISABLED),
> which preserves the PMI bit and fixes the WARNING. The additional
> work it does (__hard_irq_disable(), PACA_IRQ_HARD_DIS |=) is
> redundant but safe since both are already set at this point in the
> exit path; the trace_hardirqs_off() inside is guarded by
> if (!arch_irqs_disabled_flags(flags)) so it will not double-fire.
>
> 2. On PPC32 (hw_irq.h:467) hard_irq_disable() maps to
> arch_local_irq_disable() -> __hard_irq_disable(), which clears
> MSR[EE] in hardware. This is exactly correct: PPC32 has no soft-mask
> PACA mechanism, so the hardware disable is the right way to satisfy
> irqentry_exit()'s requirement. This also fixes a build error on PPC32
> where irq_soft_mask_set() is only defined under CONFIG_PPC64:
>
> arch/powerpc/include/asm/entry-common.h:273: error: implicit
> declaration of function 'irq_soft_mask_set'
>
> Using hard_irq_disable() requires no #ifdef and is consistent with
> how the rest of the entry code (e.g. entry-common.h:463) handles the
> same PPC32/PPC64 split.
>
> Fixes: 334f3f6d7a16 ("powerpc/entry: Disable interrupts before irqentry_exit")
> Reported-by: Venkat Rao Bagalkote <[email protected]>
> Closes:
> https://lore.kernel.org/all/[email protected]/
> Tested-by: Venkat Rao Bagalkote <[email protected]>
> Reviewed-by: Shrikanth Hegde <[email protected]>
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
> ---
> Change log:
> V2 -> V3:
> - Revert to hard_irq_disable
> - Removed some dead code
Ignore this line.
Regards,
Mukesh
> V2: https://lore.kernel.org/all/[email protected]
> V1 -> V2:
> - Instead of using hard_irq_disable use irq_soft_mask_set
> V1: https://lore.kernel.org/all/[email protected]
> arch/powerpc/include/asm/entry-common.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/entry-common.h
> b/arch/powerpc/include/asm/entry-common.h
> index 94083516df57..80b07750b531 100644
> --- a/arch/powerpc/include/asm/entry-common.h
> +++ b/arch/powerpc/include/asm/entry-common.h
> @@ -270,7 +270,7 @@ static inline void arch_interrupt_exit_prepare(struct
> pt_regs *regs)
> }
>
> /* irqentry_exit expects to be called with interrupts disabled */
> - local_irq_disable();
> + hard_irq_disable();
> }
>
> static inline void arch_interrupt_async_enter_prepare(struct pt_regs *regs)
> --
> 2.55.0
>
