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Date:   Fri, 19 Feb 2021 18:26:41 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Hector Martin <marcan@...can.st>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 7/8 v1.5] arm64: Always keep DAIF.[IF] in sync

On Sat, Feb 20, 2021 at 02:25:30AM +0900, Hector Martin wrote:
> Apple SoCs (A11 and newer) have some interrupt sources hardwired to the
> FIQ line. We implement support for this by simply treating IRQs and FIQs
> the same way in the interrupt vectors.
> 
> To support these systems, the FIQ mask bit needs to be kept in sync with
> the IRQ mask bit, so both kinds of exceptions are masked together. No
> other platforms should be delivering FIQ exceptions right now, and we
> already unmask FIQ in normal process context, so this should not have an
> effect on other systems - if spurious FIQs were arriving, they would
> already panic the kernel.

This looks good to me; I've picked this up and pushed out my arm64/fiq
branch [1,2] incorporating this, tagged as arm64-fiq-20210219.

I'll give this version a few days to gather comments before I post a v2.

[1] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git arm64/fiq
[2] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/fiqA

Thanks,
Mark.

> 
> Signed-off-by: Hector Martin <marcan@...can.st>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: James Morse <james.morse@....com>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Will Deacon <will@...nel.org>
> 
> ---
>  arch/arm64/include/asm/arch_gicv3.h |  2 +-
>  arch/arm64/include/asm/assembler.h  |  8 ++++----
>  arch/arm64/include/asm/daifflags.h  | 10 +++++-----
>  arch/arm64/include/asm/irqflags.h   | 16 +++++++---------
>  arch/arm64/kernel/entry.S           | 12 +++++++-----
>  arch/arm64/kernel/process.c         |  2 +-
>  arch/arm64/kernel/smp.c             |  1 +
>  7 files changed, 26 insertions(+), 25 deletions(-)
> 
> This is the updated patch after addressing the comments in the original
> v2 review; we're moving it to this series now, so please review it in
> this context.
> 
> diff --git a/arch/arm64/include/asm/arch_gicv3.h b/arch/arm64/include/asm/arch_gicv3.h
> index 880b9054d75c..934b9be582d2 100644
> --- a/arch/arm64/include/asm/arch_gicv3.h
> +++ b/arch/arm64/include/asm/arch_gicv3.h
> @@ -173,7 +173,7 @@ static inline void gic_pmr_mask_irqs(void)
> 
>  static inline void gic_arch_enable_irqs(void)
>  {
> -	asm volatile ("msr daifclr, #2" : : : "memory");
> +	asm volatile ("msr daifclr, #3" : : : "memory");
>  }
> 
>  #endif /* __ASSEMBLY__ */
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index bf125c591116..53ff8c71eed7 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -40,9 +40,9 @@
>  	msr	daif, \flags
>  	.endm
> 
> -	/* IRQ is the lowest priority flag, unconditionally unmask the rest. */
> -	.macro enable_da_f
> -	msr	daifclr, #(8 | 4 | 1)
> +	/* IRQ/FIQ are the lowest priority flags, unconditionally unmask the rest. */
> +	.macro enable_da
> +	msr	daifclr, #(8 | 4)
>  	.endm
> 
>  /*
> @@ -50,7 +50,7 @@
>   */
>  	.macro	save_and_disable_irq, flags
>  	mrs	\flags, daif
> -	msr	daifset, #2
> +	msr	daifset, #3
>  	.endm
> 
>  	.macro	restore_irq, flags
> diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
> index 1c26d7baa67f..5eb7af9c4557 100644
> --- a/arch/arm64/include/asm/daifflags.h
> +++ b/arch/arm64/include/asm/daifflags.h
> @@ -13,8 +13,8 @@
>  #include <asm/ptrace.h>
> 
>  #define DAIF_PROCCTX		0
> -#define DAIF_PROCCTX_NOIRQ	PSR_I_BIT
> -#define DAIF_ERRCTX		(PSR_I_BIT | PSR_A_BIT)
> +#define DAIF_PROCCTX_NOIRQ	(PSR_I_BIT | PSR_F_BIT)
> +#define DAIF_ERRCTX		(PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
>  #define DAIF_MASK		(PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
> 
> 
> @@ -47,7 +47,7 @@ static inline unsigned long local_daif_save_flags(void)
>  	if (system_uses_irq_prio_masking()) {
>  		/* If IRQs are masked with PMR, reflect it in the flags */
>  		if (read_sysreg_s(SYS_ICC_PMR_EL1) != GIC_PRIO_IRQON)
> -			flags |= PSR_I_BIT;
> +			flags |= PSR_I_BIT | PSR_F_BIT;
>  	}
> 
>  	return flags;
> @@ -69,7 +69,7 @@ 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));
> +		(read_sysreg(daif) & (PSR_I_BIT | PSR_F_BIT)) != (PSR_I_BIT | PSR_F_BIT));
> 
>  	if (!irq_disabled) {
>  		trace_hardirqs_on();
> @@ -86,7 +86,7 @@ static inline void local_daif_restore(unsigned long flags)
>  			 * If interrupts are disabled but we can take
>  			 * asynchronous errors, we can take NMIs
>  			 */
> -			flags &= ~PSR_I_BIT;
> +			flags &= ~(PSR_I_BIT | PSR_F_BIT);
>  			pmr = GIC_PRIO_IRQOFF;
>  		} else {
>  			pmr = GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET;
> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index ff328e5bbb75..b57b9b1e4344 100644
> --- a/arch/arm64/include/asm/irqflags.h
> +++ b/arch/arm64/include/asm/irqflags.h
> @@ -12,15 +12,13 @@
> 
>  /*
>   * Aarch64 has flags for masking: Debug, Asynchronous (serror), Interrupts and
> - * FIQ exceptions, in the 'daif' register. We mask and unmask them in 'dai'
> + * FIQ exceptions, in the 'daif' register. We mask and unmask them in 'daif'
>   * order:
>   * Masking debug exceptions causes all other exceptions to be masked too/
> - * Masking SError masks irq, but not debug exceptions. Masking irqs has no
> - * side effects for other flags. Keeping to this order makes it easier for
> - * entry.S to know which exceptions should be unmasked.
> - *
> - * FIQ is never expected, but we mask it when we disable debug exceptions, and
> - * unmask it at all other times.
> + * Masking SError masks IRQ/FIQ, but not debug exceptions. IRQ and FIQ are
> + * always masked and unmasked together, and have no side effects for other
> + * flags. Keeping to this order makes it easier for entry.S to know which
> + * exceptions should be unmasked.
>   */
> 
>  /*
> @@ -35,7 +33,7 @@ static inline void arch_local_irq_enable(void)
>  	}
> 
>  	asm volatile(ALTERNATIVE(
> -		"msr	daifclr, #2		// arch_local_irq_enable",
> +		"msr	daifclr, #3		// arch_local_irq_enable",
>  		__msr_s(SYS_ICC_PMR_EL1, "%0"),
>  		ARM64_HAS_IRQ_PRIO_MASKING)
>  		:
> @@ -54,7 +52,7 @@ static inline void arch_local_irq_disable(void)
>  	}
> 
>  	asm volatile(ALTERNATIVE(
> -		"msr	daifset, #2		// arch_local_irq_disable",
> +		"msr	daifset, #3		// arch_local_irq_disable",
>  		__msr_s(SYS_ICC_PMR_EL1, "%0"),
>  		ARM64_HAS_IRQ_PRIO_MASKING)
>  		:
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index acc677672277..af04ce5088ca 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -533,7 +533,7 @@ alternative_endif
> 
>  	.macro el1_interrupt_handler, handler:req
>  	gic_prio_irq_setup pmr=x20, tmp=x1
> -	enable_da_f
> +	enable_da
> 
>  	mov	x0, sp
>  	bl	enter_el1_irq_or_nmi
> @@ -544,8 +544,10 @@ alternative_endif
>  	ldr	x24, [tsk, #TSK_TI_PREEMPT]	// get preempt count
>  alternative_if ARM64_HAS_IRQ_PRIO_MASKING
>  	/*
> -	 * DA_F were cleared at start of handling. If anything is set in DAIF,
> -	 * we come back from an NMI, so skip preemption
> +	 * DA were cleared at start of handling, and IF are cleared by
> +	 * the GIC irqchip driver using gic_arch_enable_irqs() for
> +	 * normal IRQs. If anything is set, it means we come back from
> +	 * an NMI instead of a normal IRQ, so skip preemption
>  	 */
>  	mrs	x0, daif
>  	orr	x24, x24, x0
> @@ -562,7 +564,7 @@ alternative_else_nop_endif
>  	.macro el0_interrupt_handler, handler:req
>  	gic_prio_irq_setup pmr=x20, tmp=x0
>  	user_exit_irqoff
> -	enable_da_f
> +	enable_da
> 
>  	tbz	x22, #55, 1f
>  	bl	do_el0_irq_bp_hardening
> @@ -763,7 +765,7 @@ el0_error_naked:
>  	mov	x0, sp
>  	mov	x1, x25
>  	bl	do_serror
> -	enable_da_f
> +	enable_da
>  	b	ret_to_user
>  SYM_CODE_END(el0_error)
> 
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 6616486a58fe..34ec400288d0 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -84,7 +84,7 @@ static void noinstr __cpu_do_idle_irqprio(void)
>  	unsigned long daif_bits;
> 
>  	daif_bits = read_sysreg(daif);
> -	write_sysreg(daif_bits | PSR_I_BIT, daif);
> +	write_sysreg(daif_bits | PSR_I_BIT | PSR_F_BIT, daif);
> 
>  	/*
>  	 * Unmask PMR before going idle to make sure interrupts can
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index ad00f99ee9b0..9dee8a17b1ac 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -188,6 +188,7 @@ static void init_gic_priority_masking(void)
>  	cpuflags = read_sysreg(daif);
> 
>  	WARN_ON(!(cpuflags & PSR_I_BIT));
> +	WARN_ON(!(cpuflags & PSR_F_BIT));
> 
>  	gic_write_pmr(GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET);
>  }
> --
> 2.30.0
> 

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