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

[Vladimir Murzin <vladimir.murzin@arm.com>]

On 7/10/26 08:44, Jinjie Ruan wrote:
> 
> 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.
>>
>> 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)
> Maybe switch_to_pmr_masking()?
> 

I have no strong opinion on that, tbh.

Having another look at the code made me think that this helper has
only a single caller. Perhaps we should move the system_uses_irq_prio_masking()
check from the caller into the helper, making it clear that the helper
is specific to pNMI without having to inspect the call site.

What do you reckon?

>> +{
>> +	WARN_ON(read_sysreg(daif) & PSR_A_BIT);
>> +	lockdep_assert_irqs_disabled();
>> +
>> +	gic_write_pmr(GIC_PRIO_IRQOFF);
>> +	write_sysreg(DAIF_PROCCTX, daif);
> otherwise LGTM
> Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
> 

Thanks!

Vladimir

>> +}
>> +
>>  #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();
>>  	}
>>  }
>