Re: [PATCH 15/17] arm64/nmi: Add handling of superpriority interrupts as NMIs

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The early return for superpriority NMIs in `el1_interrupt()` skips restoring the DAIF exception mask, leaving Debug and SError exceptions unmasked during the kernel exception exit sequence.
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commit d42506f146936c84b19bd8abaf9cf4045e0c586d
Author: Mark Brown <broonie@kernel.org>

arm64/nmi: Add handling of superpriority interrupts as NMIs

This commit introduces superpriority interrupts as NMIs to allow prompt
handling of time-critical interrupts. It updates EL1 and EL0 interrupt entry
paths to check isr_el1 for superpriority status before unmasking normal
interrupts, routing them to newly added root handlers.

Link: https://lore.kernel.org/r/20221112151708.175147-13-broonie@kernel.org

> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
> index dc223085e7735..4115a5e7c3925 100644
> --- a/arch/arm64/kernel/entry-common.c
> +++ b/arch/arm64/kernel/entry-common.c
[ ... ]
> @@ -537,11 +549,20 @@ static __always_inline void __el1_irq(struct pt_regs *regs,
>  
>  	arm64_exit_to_kernel_mode(regs, state);
>  }
> -static void noinstr el1_interrupt(struct pt_regs *regs,
> -				  void (*handler)(struct pt_regs *))
> +static void noinstr el1_interrupt(struct pt_regs *regs, u64 nmi_flag,
> +				  void (*handler)(struct pt_regs *),
> +				  void (*nmi_handler)(struct pt_regs *))
>  {
>  	struct exception_mask mask = irq_entry_unmask_debug_serror(regs);
>  
> +	if (system_uses_nmi()) {
> +		/* Is there a NMI to handle? */
> +		if (read_sysreg(isr_el1) & nmi_flag) {
> +			__el1_nmi(regs, nmi_handler);
> +			return;

[Severity: High]
Does this early return path in el1_interrupt() bypass the required
exception_exit_restore_mask(mask) call at the end of the function?

It looks like this might leave Debug and SError exceptions unmasked during the
kernel exception exit sequence. If an asynchronous SError or hardware
breakpoint triggers during the assembly exception return sequence after this
point, it could clobber the exception state and cause a fatal recursive fault.

> +		}
> +	}
> +
>  	if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && regs_irqs_disabled(regs))
>  		__el1_pnmi(regs, handler);
>  	else

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260703100135.2512312-1-ruanjinjie@huawei.com?part=15