linux-kernel - Re: [PATCH v3 6/8] arm64: irqflags: Introduce explicit debugging for IRQ priorities

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Date:   Fri, 7 Jun 2019 17:31:26 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Julien Thierry <julien.thierry@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        yuzenghui@...wei.com, wanghaibin.wang@...wei.com,
        james.morse@....com, will.deacon@....com, catalin.marinas@....com,
        mark.rutland@....com, liwei391@...wei.com
Subject: Re: [PATCH v3 6/8] arm64: irqflags: Introduce explicit debugging for
 IRQ priorities

On 06/06/2019 10:31, Julien Thierry wrote:
> Using IRQ priority masking to enable/disable interrupts is a bit
> sensitive as it requires to deal with both ICC_PMR_EL1 and PSR.I.
> 
> Introduce some validity checks to both highlight the states in which
> functions dealing with IRQ enabling/disabling can (not) be called, and
> bark a warning when called in an unexpected state.
> 
> Since these checks are done on hotpaths, introduce a build option to
> choose whether to do the checking.
> 
> Signed-off-by: Julien Thierry <julien.thierry@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> ---
>  arch/arm64/Kconfig                  | 11 +++++++++++
>  arch/arm64/include/asm/cpufeature.h |  6 ++++++
>  arch/arm64/include/asm/daifflags.h  |  7 +++++++
>  arch/arm64/include/asm/irqflags.h   | 14 +++++++++++++-
>  4 files changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 697ea05..8acc40e 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1436,6 +1436,17 @@ config ARM64_PSEUDO_NMI
> 
>  	  If unsure, say N
> 
> +if ARM64_PSEUDO_NMI
> +config ARM64_DEBUG_PRIORITY_MASKING
> +	bool "Debug interrupt priority masking"
> +	help
> +	  This adds runtime checks to functions enabling/disabling
> +	  interrupts when using priority masking. The additional checks verify
> +	  the validity of ICC_PMR_EL1 when calling concerned functions.
> +
> +	  If unsure, say N
> +endif
> +
>  config RELOCATABLE
>  	bool
>  	help
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index bc895c8..693a086 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -617,6 +617,12 @@ static inline bool system_uses_irq_prio_masking(void)
>  	       cpus_have_const_cap(ARM64_HAS_IRQ_PRIO_MASKING);
>  }
> 
> +static inline bool system_has_prio_mask_debugging(void)
> +{
> +	return IS_ENABLED(CONFIG_ARM64_DEBUG_PRIORITY_MASKING) &&
> +	       system_uses_irq_prio_masking();
> +}
> +
>  #define ARM64_SSBD_UNKNOWN		-1
>  #define ARM64_SSBD_FORCE_DISABLE	0
>  #define ARM64_SSBD_KERNEL		1
> diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
> index f93204f..eca5bee 100644
> --- a/arch/arm64/include/asm/daifflags.h
> +++ b/arch/arm64/include/asm/daifflags.h
> @@ -28,6 +28,10 @@
>  /* mask/save/unmask/restore all exceptions, including interrupts. */
>  static inline void local_daif_mask(void)
>  {
> +	WARN_ON(system_has_prio_mask_debugging() &&
> +		(read_sysreg_s(SYS_ICC_PMR_EL1) == (GIC_PRIO_IRQOFF |
> +						    GIC_PRIO_PSR_I_SET)));
> +
>  	asm volatile(
>  		"msr	daifset, #0xf		// local_daif_mask\n"
>  		:
> @@ -62,6 +66,9 @@ static inline void local_daif_restore(unsigned long flags)
>  {
>  	bool irq_disabled = flags & PSR_I_BIT;
> 
> +	WARN_ON(system_has_prio_mask_debugging() &&
> +		!(read_sysreg(daif) & PSR_I_BIT));
> +
>  	if (!irq_disabled) {
>  		trace_hardirqs_on();
> 
> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index b6f757f..cac2d2a 100644
> --- a/arch/arm64/include/asm/irqflags.h
> +++ b/arch/arm64/include/asm/irqflags.h
> @@ -40,6 +40,12 @@
>   */
>  static inline void arch_local_irq_enable(void)
>  {
> +	if (system_has_prio_mask_debugging()) {
> +		u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
> +
> +		WARN_ON_ONCE(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
> +	}
> +
>  	asm volatile(ALTERNATIVE(
>  		"msr	daifclr, #2		// arch_local_irq_enable\n"
>  		"nop",
> @@ -53,6 +59,12 @@ static inline void arch_local_irq_enable(void)
> 
>  static inline void arch_local_irq_disable(void)
>  {
> +	if (system_has_prio_mask_debugging()) {
> +		u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
> +
> +		WARN_ON_ONCE(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
> +	}
> +
>  	asm volatile(ALTERNATIVE(
>  		"msr	daifset, #2		// arch_local_irq_disable",
>  		__msr_s(SYS_ICC_PMR_EL1, "%0"),
> @@ -86,7 +98,7 @@ static inline int arch_irqs_disabled_flags(unsigned long flags)
> 
>  	asm volatile(ALTERNATIVE(
>  		"and	%w0, %w1, #" __stringify(PSR_I_BIT),
> -		"eor	%w0, %w1, #" __stringify(GIC_PRIO_IRQOFF),
> +		"eor	%w0, %w1, #" __stringify(GIC_PRIO_IRQON),

Err... Which version is the correct one? This one, or the previous one?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...