Re: [RFC PATCH 07/36] arm64: entry: mask DAIF before returning from C EL1 handlers

[Jinjie Ruan <ruanjinjie@huawei.com>]

On 7/9/2026 8:13 PM, Vladimir Murzin wrote:
> From: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> 
> Most EL1 exceptions already call `local_daif_mask()` before returning,
> with the exception of debug exception handlers which do not change
> DAIF, and the IRQ/FIQ/Error handlers.
> 
> However, DAIF get masked in `kernel_exit()` in all cases when
> returning from EL1 C handlers anyway.
> 
> Move this masking from assembly to C by adding `local_daif_mask()`
> before `irqentry_nmi_exit()` when it is called by EL1 handlers.
> 
> Remove the `disable_daif` assembly macro, as this was its only use.
> 
> Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
> ---
>  arch/arm64/include/asm/assembler.h | 4 ----
>  arch/arm64/kernel/entry-common.c   | 2 ++
>  arch/arm64/kernel/entry.S          | 4 ----
>  3 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index effae53e9739..0b58b550e8dc 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -34,10 +34,6 @@
>  	wx\n	.req	w\n
>  	.endr
>  
> -	.macro disable_daif
> -	msr	daifset, #0xf
> -	.endm
> -
>  /*
>   * Save/restore interrupts.
>   */
> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
> index ceb4eb11232a..2be42d7f4eaa 100644
> --- a/arch/arm64/kernel/entry-common.c
> +++ b/arch/arm64/kernel/entry-common.c
> @@ -495,6 +495,7 @@ static __always_inline void __el1_pnmi(struct pt_regs *regs,
>  
>  	state = irqentry_nmi_enter(regs);
>  	do_interrupt_handler(regs, handler);
> +	local_daif_mask();
>  	irqentry_nmi_exit(regs, state);
>  }
>  
> @@ -540,6 +541,7 @@ asmlinkage void noinstr el1h_64_error_handler(struct pt_regs *regs)
>  	local_daif_restore(DAIF_ERRCTX);
>  	state = irqentry_nmi_enter(regs);
>  	do_serror(regs, esr);
> +	local_daif_mask();
>  	irqentry_nmi_exit(regs, state);

This is similar to my patch below:

https://lore.kernel.org/all/20260703100135.2512312-4-ruanjinjie@huawei.com/

I think there are at least three problems：

1、disable_daif is missing for el1h_64_sync_handler() and __el1_irq()

2、The order after moving to the C code is incorrect. disable_daif should
be the exit point for C, that is, after irqentry_nmi_exit(), it is
unclear why this order change occurred ?

3、local_daif_mask () has added some pseudo NMI operations and
trace_hardirqs_off ().

>  }
>  
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index e0db14e9c843..f63049ac32dc 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -333,10 +333,6 @@ alternative_else_nop_endif
>  	.endm
>  
>  	.macro	kernel_exit, el
> -	.if	\el != 0
> -	disable_daif
> -	.endif
> -
>  #ifdef CONFIG_ARM64_PSEUDO_NMI
>  alternative_if_not ARM64_HAS_GIC_PRIO_MASKING
>  	b	.Lskip_pmr_restore\@