Re: [PATCH 06/38] arm64: entry: replace DAIF helpers with entry helpers

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

On 9/16/26 10:34, Jinjie Ruan wrote:
> 
> 在 2026/9/14 18:20, Vladimir Murzin 写道:
>> From: Ada Couprie Diaz <ada.coupriediaz@arm.com>
>>
>> Replace all uses of the `local_daif_...` helpers in `entry-common.c`
>> with the new entry-specific exception masking helpers.
>>
>> Also replace `local_irq_disable()` with a switch to NOIRQ context
>> using the new helpers. This provides:
>>
>> - consistency checks for hardware state
>> - a unified style for managing exception context
>>
>> Now that both the irqflags API and entry code handle DAIF and PMR
>> correctly, remove `GIC_PRIO_PSR_I_SET` from the PMR value set by
>> `kernel_entry` in `entry.S` and by `init_gic_priority_masking()` in
>> `kernel/smp.c`.
>>
>> The `local_daif_...` helpers and other specialized code still use
>> `GIC_PRIO_PSR_I_SET` for now; this commit does not change their
>> behavior.
>>
>> Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
>> Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
>> ---
>>  arch/arm64/kernel/entry-common.c | 258 ++++++++++++++++++++-----------
>>  arch/arm64/kernel/entry.S        |   2 +-
>>  arch/arm64/kernel/smp.c          |   2 +-
>>  3 files changed, 173 insertions(+), 89 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
>> index 72c03ccea59f..fd0bfead6e70 100644
>> --- a/arch/arm64/kernel/entry-common.c
>> +++ b/arch/arm64/kernel/entry-common.c
>> @@ -18,11 +18,11 @@
>>  #include <linux/thread_info.h>
>>  
>>  #include <asm/cpufeature.h>
>> -#include <asm/daifflags.h>
>>  #include <asm/esr.h>
>>  #include <asm/exception.h>
>>  #include <asm/fpsimd.h>
>>  #include <asm/irq_regs.h>
>> +#include <asm/interrupts/entry.h>
>>  #include <asm/kprobes.h>
>>  #include <asm/mmu.h>
>>  #include <asm/processor.h>
>> @@ -53,9 +53,10 @@ static noinstr irqentry_state_t arm64_enter_from_kernel_mode(struct pt_regs *reg
>>   * instrumentable code, or any code which may trigger an exception.
>>   */
>>  static void noinstr __arm64_exit_to_kernel_mode(struct pt_regs *regs,
>> -						irqentry_state_t state)
>> +						irqentry_state_t state,
>> +						arm64_exc_hwstate_t hwstate)
>>  {
>> -	local_daif_mask();
>> +	arm64_mask_exc_context(hwstate);
>>  	mte_check_tfsr_exit();
>>  	irqentry_exit_to_kernel_mode_after_preempt(regs, state);
>>  }
>> @@ -64,22 +65,24 @@ static void noinstr __arm64_exit_to_kernel_mode(struct pt_regs *regs,
>>   * We are returning from the context which allows involuntary kernel preemption
>>   */
>>  static void noinstr arm64_exit_to_kernel_mode_preempt(struct pt_regs *regs,
>> -						      irqentry_state_t state)
>> +						      irqentry_state_t state,
>> +						      arm64_exc_hwstate_t hwstate)
>>  {
>>  	irqentry_exit_to_kernel_mode_preempt(regs, state);
>> -	__arm64_exit_to_kernel_mode(regs, state);
>> +	__arm64_exit_to_kernel_mode(regs, state, hwstate);
>>  }
>>  
>>  static void noinstr arm64_exit_to_kernel_mode(struct pt_regs *regs,
>> -					      irqentry_state_t state)
>> +					      irqentry_state_t state,
>> +					      arm64_exc_hwstate_t hwstate)
>>  {
>>  	if (!regs_irqs_disabled(regs)) {
>> -		local_irq_disable();
>> -		arm64_exit_to_kernel_mode_preempt(regs, state);
>> +		hwstate = arm64_lift_exc_context(hwstate, NOIRQ_CONTEXT);
> Hi Vladimir,
> 
> As we discussed earlier in the link below, I think it is neither
> necessary nor correct to switch to NOIRQ_CONTEXT here; the default
> local_irq_disable() is fine.
> 

Hi Jinjie,

Switching to NOIRQ_CONTEXT *unconditionally* is indeed incorrect, but
here we do it only if !regs_irqs_disabled(regs), which implies that
DAIF is 0.  Thus, switching to NOIRQ_CONTEXT is equivalent to
local_irq_disable().

I'd prefer not to mix different APIs and to keep the switch to
NOIRQ_CONTEXT, since this provides:
- consistency checks for the hardware state
- a unified style for managing exception context

If that makes this clearer we can replace regs_irqs_disabled(regs)
with arch_irqs_disabled_flags(hwstate.flags).

Thanks
Vladimir


> Link:
> https://lore.kernel.org/all/77080aa8-7df1-43f0-8c82-1096db05f745@huawei.com/
> 
> Best regards,
> Jinjie
>