[RFC PATCH v2 14/45] arm64: entry: Introduce entry specific exception masking helpers

[Vladimir Murzin]

On 7/28/26 09:48, Jinjie Ruan wrote:
> 
> 在 2026/7/28 0:34, Vladimir Murzin 写道:
>> From: Ada Couprie Diaz <ada.coupriediaz at arm.com>
>>
>> The entry code handles interrupt masking differently from the rest of
>> the kernel. Exception handlers enter and exit with all exceptions
>> masked, but they must temporarily unmask the appropriate set of
>> exceptions so that the rest of the handler executes with the expected
>> exception state.
>>
>> For EL0 handlers, this means dropping to masking context appropriate
>> for the work to be performed. For EL1 handlers, this means restoring
>> the masking context of the interrupted task. In both cases, all
>> exceptions must be masked again before returning from the exception
>> handler.
>>
>> The rest of the kernel typically follows the opposite pattern: it
>> raises the masking context to protect a critical section and later
>> restores the previous context.
>>
>> Given these different usage patterns, introduce a dedicated set of
>> exception masking helpers for the entry code. Keeping these helpers
>> separate from the generic interrupt masking APIs makes the intended
>> usage explicit and helps avoid mixing the two masking models.
>>
>> Signed-off-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
>> ---
>>  arch/arm64/include/asm/interrupts/entry.h | 113 ++++++++++++++++++++++
>>  1 file changed, 113 insertions(+)
>>  create mode 100644 arch/arm64/include/asm/interrupts/entry.h
>>
>> diff --git a/arch/arm64/include/asm/interrupts/entry.h b/arch/arm64/include/asm/interrupts/entry.h
>> new file mode 100644
>> index 000000000000..d66eb5d633f0
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/interrupts/entry.h
>> @@ -0,0 +1,113 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Copyright (C) 2025 Arm Ltd.
>> + */
>> +#ifndef __ASM_INTERRUPTS_ENTRY_H
>> +#define __ASM_INTERRUPTS_ENTRY_H
>> +
>> +#include <asm/arch_gicv3.h>
>> +#include <asm/bug.h>
>> +#include <asm/cpufeature.h>
>> +#include <asm/interrupts/common_flags.h>
>> +
>> +
> [...]
>> +static __always_inline
>> +arm64_exc_hwstate_t arm64_drop_exc_context(arm64_exc_hwstate_t prev, arm64_exc_context_t context)
>> +{
>> +	arm64_exc_hwstate_t next = arm64_exc_hwstate_of_context(context);
>> +
>> +	if (IS_ENABLED(CONFIG_DEBUG_IRQFLAGS)) {
>> +		bool pnmi = system_uses_irq_prio_masking();
>> +
>> +		WARN_ON_ONCE(context > ERROR_CONTEXT &&
>> +			     prev.daif == DAIF_ERRCTX);
>> +
>> +		WARN_ON_ONCE(context > NONMI_CONTEXT &&
>> +			     prev.daif == DAIF_PROCCTX_NOIRQ);
>> +
>> +		WARN_ON_ONCE(context > NOIRQ_CONTEXT &&
>> +			     pnmi && prev.pmr == GIC_PRIO_IRQOFF);
>> +
>> +		WARN_ON_ONCE(context > PROCESS_CONTEXT &&
>> +			     ((pnmi && prev.daif == DAIF_PROCCTX && prev.pmr == GIC_PRIO_IRQON) ||
>> +			      (!pnmi && prev.daif == DAIF_PROCCTX)));
>> +	}
>> +
>> +	return __arm64_switch_exc_hwstate_to(prev, next);
>> +}
>> +
>> +static __always_inline
>> +arm64_exc_hwstate_t arm64_lift_exc_context(arm64_exc_hwstate_t prev, arm64_exc_context_t context)
>> +{
>> +	arm64_exc_hwstate_t next = arm64_exc_hwstate_of_context(context);
>> +
>> +	if (IS_ENABLED(CONFIG_DEBUG_IRQFLAGS)) {
>> +		bool pnmi = system_uses_irq_prio_masking();
>> +
>> +		WARN_ON_ONCE(context < CRITICAL_CONTEXT &&
>> +			     prev.daif == DAIF_MASK);
>> +
>> +		WARN_ON_ONCE(context < ERROR_CONTEXT &&
>> +			     prev.daif == DAIF_ERRCTX);
>> +
>> +		WARN_ON_ONCE(context < NONMI_CONTEXT &&
>> +			     pnmi && prev.daif == DAIF_PROCCTX_NOIRQ);
>> +
>> +		WARN_ON_ONCE(context < NOIRQ_CONTEXT &&
>> +			     ((pnmi && prev.pmr == GIC_PRIO_IRQOFF) ||
>> +			      (!pnmi && prev.daif == DAIF_PROCCTX_NOIRQ)));
>> +	}
>> +
>> +	return __arm64_switch_exc_hwstate_to(prev, next);

Hi Jinjie,

> Hi Vladimir,
> 
> These two functions appear to have similar functionality, with only the
> debug code being different. Can they be merged?
> 

Functionality is indeed similar, but the intent is different. It
gently encourages the user to think about the exception context they
are currently in, which should make it easier to reason about
exception transitions. That is not always possible with a merged "take
me there" interface.

The debug code then ensures that the requested exception transition is
in the correct direction.

Cheers
Vladimir

>> +}
>> +
>> +
>> +static __always_inline
>> +arm64_exc_hwstate_t arm64_unmask_exc_context(arm64_exc_context_t context)
>> +{
>> +	arm64_exc_hwstate_t prev = arm64_exc_hwstate_of_context(CRITICAL_CONTEXT);
>> +
>> +	return arm64_drop_exc_context(prev, context);
>> +}
>> +
>> +static __always_inline
>> +arm64_exc_hwstate_t arm64_mask_exc_context(arm64_exc_hwstate_t prev)
>> +{
>> +	return arm64_lift_exc_context(prev, CRITICAL_CONTEXT);
>> +}
> otherwise, LGTM
> Reviewed-by: Jinjie Ruan <ruanjinjie at huawei.com>
> 
>> +
>> +#endif /* __ASM_INTERRUPTS_ENTRY_H */
>