Re: [PATCH 05/38] arm64: entry: Introduce entry specific exception masking helpers

[Jinjie Ruan <ruanjinjie@huawei.com>]

在 2026/9/14 18:20, Vladimir Murzin 写道:
> From: Ada Couprie Diaz <ada.coupriediaz@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@arm.com>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
> Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
> ---
>  arch/arm64/include/asm/interrupts/entry.h | 100 ++++++++++++++++++++++
>  1 file changed, 100 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..0cfca62aa25b
> --- /dev/null
> +++ b/arch/arm64/include/asm/interrupts/entry.h
> @@ -0,0 +1,100 @@
> +/* 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_switch_exc_hwstate_to(arm64_exc_hwstate_t prev,
> +						  arm64_exc_hwstate_t next)
> +{
> +	bool irqs_disabled = arch_irqs_disabled_flags(next.flags);
> +	bool force;
> +
> +	arm64_debug_exc_hwstate(prev);
> +
> +	if (prev.flags == next.flags)
> +		return next;
> +
> +	if (!irqs_disabled)
> +		trace_hardirqs_on();
> +
> +	force = system_uses_irq_prio_masking() && prev.pmr != next.pmr;
> +
> +	__arm64_update_exc_hwstate(next, force);
> +
> +	if (irqs_disabled)
> +		trace_hardirqs_off();
> +
> +	return next;
> +}
> +
> +static __always_inline
> +arm64_exc_hwstate_t arm64_inherit_exc_context(struct pt_regs *regs)
> +{
> +	arm64_exc_hwstate_t prev = arm64_exc_hwstate_of_context(CRITICAL_CONTEXT);
> +	arm64_exc_hwstate_t next = arm64_inherit_exc_hwstate(regs);

Could it be renamed to a more intuitive name, such as
arm64_exc_hwstate_of_regs()?

> +
> +	return __arm64_switch_exc_hwstate_to(prev, next);
> +}
> +
> +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)) {
> +		WARN_ON_ONCE(prev.daif < next.daif);
> +
> +		if (prev.daif == next.daif) {
> +			/*
> +			 * GIC_PRIO_IRQON is larger that GIC_PRIO_IRQOFF so larger PMR value is weaker
> +			 */
> +			WARN_ON_ONCE(system_uses_irq_prio_masking() && prev.pmr > next.pmr);
> +		}

The if branch is a dead code now, we can remove it.

arm64_drop_exc_context is only used directly in the context of
el0t_64_error_handler below. It switches from ERROR_CONTEXT to
PROCESS_CONTEXT.

And now arm64_unmask_exc_context always switch from CRITICAL_CONTEXT
to ERROR_CONTEXT/NONMI_CONTEXT/NOIRQ_CONTEXT/PROCESS_CONTEXT.

So there is no case where prev and next DAIF are the same.

1009 static void noinstr __el0_error_handler_common(struct pt_regs *regs)
1010 {
1011 >-------unsigned long esr = read_sysreg(esr_el1);
1012 >-------arm64_exc_hwstate_t hwstate;
1013 >-------irqentry_state_t state;
1014
1015 >-------arm64_enter_from_user_mode(regs);
1016 >-------hwstate = arm64_unmask_exc_context(ERROR_CONTEXT);
1017 >-------state = irqentry_nmi_enter(regs);
1018 >-------do_serror(regs, esr);
1019 >-------irqentry_nmi_exit(regs, state);
1020 >-------hwstate = arm64_drop_exc_context(hwstate, PROCESS_CONTEXT);
1021 >-------arm64_exit_to_user_mode(regs, hwstate);
1022 >-------arm64_debug_exc_context(CRITICAL_CONTEXT);
1023 }
1024
1025 asmlinkage void noinstr el0t_64_error_handler(struct pt_regs *regs)
1026 {
1027 >-------__el0_error_handler_common(regs);
1028 }


> +	}
> +
> +	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)) {
> +		WARN_ON_ONCE(prev.daif > next.daif);
> +
> +		if (prev.daif == next.daif) {
> +			/*
> +			 * GIC_PRIO_IRQON is larger that GIC_PRIO_IRQOFF so smaller PMR value is stronger
> +			 */
> +			WARN_ON_ONCE(system_uses_irq_prio_masking() && prev.pmr < next.pmr);
> +		}
> +	}
> +
> +	return __arm64_switch_exc_hwstate_to(prev, next);
> +}
> +
> +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);
> +}
> +
> +#endif /* __ASM_INTERRUPTS_ENTRY_H */

-- 
Best regards,
Jinjie