Re: [RFC PATCH v2 10/45] arm64: irqflags: Introduce arm64-specific irqflags type

[Jinjie Ruan <ruanjinjie@huawei.com>]

在 2026/7/28 0:34, Vladimir Murzin 写道:
> From: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> 
> With pseudo-NMIs enabled, we have two mechanisms that control
> interrupt masking in parallel :
> - The DAIF flags, masking at the CPU
> - The GIC PMR, masking before the CPU
> 
> However, our irqflags implementation currently assumes that only one
> of the two is used at a time, so both DAIF and PMR masking use the same
> `unsigned long flags` in their own way.
> This is incorrect, as some parts of the kernel will mask interrupts
> with DAIF directly or bypass the local_irq masking via the PMR,
> and makes tracking the state and changes of both in parallel impossible.
> 
> The irqflags API expects `unsigned long`s to be passed around, but
> they should not be manipulated outside of the arch-specific code.
> So, we can encode the information we need however we want as long as
> we return and accept `unsigned long`s.
> 
> Introduce a union type for arm64 irqflags whose first member is
> a struct allowing us to track DAIF and PMR in parallel, and the second
> is the `unsigned long` expected by the irqflags API.
> 
> DAIF is a two byte value, to maintain compatibility with existing defines.
> PMR is a one byte value, which is the maximum amount of priority bits
> allowed by the GICv3 architecture.
> 
> Update the internal irqflags functions to use this new union and convert
> back and forth with the irqflags unsigned long.
> There should be no functional changes.
> 
> Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
> ---
>  arch/arm64/include/asm/irqflags.h | 43 ++++++++++++++++++++++++++-----
>  1 file changed, 37 insertions(+), 6 deletions(-)

LGTM
Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>

> 
> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index a8cb5a5c93b7..1863a955d119 100644
> --- a/arch/arm64/include/asm/irqflags.h
> +++ b/arch/arm64/include/asm/irqflags.h
> @@ -9,6 +9,8 @@
>  #include <asm/ptrace.h>
>  #include <asm/sysreg.h>
>  
> +#include <linux/compiler.h>
> +
>  /*
>   * Aarch64 has flags for masking: Debug, Asynchronous (serror), Interrupts and
>   * FIQ exceptions, in the 'daif' register. We mask and unmask them in 'daif'
> @@ -20,6 +22,23 @@
>   * exceptions should be unmasked.
>   */
>  
> + /*
> +  * Internally, we want to independently manipulate and track the different
> +  * interrupt masking mechanisms.
> +  * Externally, the generic irqflags API expects unsgined longs to represent
> +  * the state of interrupts, which are treated as obscure arch-specific data.
> +  */
> +typedef union arm64_exc_hwstate {
> +	struct {
> +		u16 daif;
> +		u8 pmr;
> +		u8 __padding[5];
> +	};
> +	unsigned long flags;
> +} arm64_exc_hwstate_t;
> +
> +static_assert(sizeof(arm64_exc_hwstate_t) == sizeof(unsigned long));
> +
>  static __always_inline void __daif_local_irq_enable(void)
>  {
>  	barrier();
> @@ -79,12 +98,16 @@ static __always_inline void arch_local_irq_disable(void)
>  
>  static __always_inline unsigned long __daif_local_save_flags(void)
>  {
> -	return read_sysreg(daif);
> +	arm64_exc_hwstate_t hwstate = { .daif = read_sysreg(daif) };
> +
> +	return hwstate.flags;
>  }
>  
>  static __always_inline unsigned long __pmr_local_save_flags(void)
>  {
> -	return read_sysreg_s(SYS_ICC_PMR_EL1);
> +	arm64_exc_hwstate_t hwstate = { .pmr = read_sysreg_s(SYS_ICC_PMR_EL1) };
> +
> +	return hwstate.flags;
>  }
>  
>  /*
> @@ -101,12 +124,16 @@ static __always_inline unsigned long arch_local_save_flags(void)
>  
>  static __always_inline bool __daif_irqs_disabled_flags(unsigned long flags)
>  {
> -	return flags & PSR_I_BIT;
> +	arm64_exc_hwstate_t hwstate = { .flags = flags };
> +
> +	return hwstate.daif & PSR_I_BIT;
>  }
>  
>  static __always_inline bool __pmr_irqs_disabled_flags(unsigned long flags)
>  {
> -	return flags != GIC_PRIO_IRQON;
> +	arm64_exc_hwstate_t hwstate = { .flags = flags };
> +
> +	return hwstate.pmr != GIC_PRIO_IRQON;
>  }
>  
>  static __always_inline bool arch_irqs_disabled_flags(unsigned long flags)
> @@ -171,15 +198,19 @@ static __always_inline unsigned long arch_local_irq_save(void)
>  
>  static __always_inline void __daif_local_irq_restore(unsigned long flags)
>  {
> +	arm64_exc_hwstate_t hwstate = { .flags = flags };
> +
>  	barrier();
> -	write_sysreg(flags, daif);
> +	write_sysreg(hwstate.daif, daif);
>  	barrier();
>  }
>  
>  static __always_inline void __pmr_local_irq_restore(unsigned long flags)
>  {
> +	arm64_exc_hwstate_t hwstate = { .flags = flags };
> +
>  	barrier();
> -	write_sysreg_s(flags, SYS_ICC_PMR_EL1);
> +	write_sysreg_s(hwstate.pmr, SYS_ICC_PMR_EL1);
>  	pmr_sync();
>  	barrier();
>  }