Re: [RFC PATCH 06/36] arm64: irq: introduce a helper for GIC priority initialization

[Jinjie Ruan <ruanjinjie@huawei.com>]

On 7/9/2026 8:13 PM, Vladimir Murzin wrote:
> From: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> 
> Arm64's `init_IRQ()` calls `local_daif_restore()` to synchronize
> interrupt masking via DAIF and switch to masking via PMR.  This
> depends on a very specific behaviour of `local_daif_restore()` which
> will clear DAIF if masking interrupts via PMR, which will get removed
> in the future.
> 
> As `setup_arch()` cleared DA only earlier, introduce a dedicated
> helper that explicitly initializes the PMR to mask interrupts and
> clears DAIF, switching to IRQ priority masking.

I believe that the `local_daif_restore(DAIF_PROCCTX_NOIRQ)` inside
`setup_arch()` should be directly replaced with the following code.
Otherwise, since the pseudo NMI has not yet taken effect at this point,
it could lead to ambiguity.

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 23c05dc7a8f2..35c5310783f4 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -311,7 +311,8 @@ void __init __no_sanitize_address setup_arch(char
**cmdline_p)
         * IRQ and FIQ will be unmasked after the root irqchip has been
         * detected and initialized.
         */
-       local_daif_restore(DAIF_PROCCTX_NOIRQ);
+       write_sysreg(DAIF_PROCCTX_NOIRQ, daif);
+       trace_hardirqs_off();



> 
> Given it is a dedicated helper, add a lockdep assertion as
> `setup_arch()` should always have called `trace_hardirqs_off()` when
> clearing DA, otherwise something bad happened.
> 
> Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
> ---
>  arch/arm64/include/asm/daifflags.h | 15 +++++++++++++++
>  arch/arm64/kernel/irq.c            |  7 +++----
>  2 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
> index 795b35128467..56341578e7e3 100644
> --- a/arch/arm64/include/asm/daifflags.h
> +++ b/arch/arm64/include/asm/daifflags.h
> @@ -141,4 +141,19 @@ static __always_inline void local_daif_inherit(struct pt_regs *regs)
>  	 */
>  	write_sysreg(flags, daif);
>  }
> +
> +/*
> + * During early boot, we unmask PSR.DA before the GIC has been set up.
> + * If we use IRQ priority masking, the PMR and PSR will be out of sync
> + * after the GIC is enabled : sync them up.
> + */
> +static inline void local_interrupt_priority_init(void)
> +{
> +	WARN_ON(read_sysreg(daif) & PSR_A_BIT);
> +	lockdep_assert_irqs_disabled();
> +
> +	gic_write_pmr(GIC_PRIO_IRQOFF);
> +	write_sysreg(DAIF_PROCCTX, daif);
> +}
> +
>  #endif
> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
> index 9fafd826002b..c73faa30268d 100644
> --- a/arch/arm64/kernel/irq.c
> +++ b/arch/arm64/kernel/irq.c
> @@ -126,10 +126,9 @@ void __init init_IRQ(void)
>  
>  	if (system_uses_irq_prio_masking()) {
>  		/*
> -		 * Now that we have a stack for our IRQ handler, set
> -		 * the PMR/PSR pair to a consistent state.
> +		 * Now that we have a stack for our IRQ handler,
> +		 * let's mask interrupts via the PMR.
>  		 */
> -		WARN_ON(read_sysreg(daif) & PSR_A_BIT);
> -		local_daif_restore(DAIF_PROCCTX_NOIRQ);
> +		local_interrupt_priority_init();
>  	}
>  }