linux-kernel - Re: [PATCH v6 10/24] arm64: irqflags: Use ICC_PMR

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Date:   Tue, 4 Dec 2018 17:36:10 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Julien Thierry <julien.thierry@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, daniel.thompson@...aro.org,
        marc.zyngier@....com, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        will.deacon@....com, linux-kernel@...r.kernel.org,
        christoffer.dall@....com, james.morse@....com,
        Oleg Nesterov <oleg@...hat.com>, joel@...lfernandes.org
Subject: Re: [PATCH v6 10/24] arm64: irqflags: Use ICC_PMR_EL1 for interrupt
 masking

On Mon, Nov 12, 2018 at 11:57:01AM +0000, Julien Thierry wrote:
> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index 24692ed..e0a32e4 100644
> --- a/arch/arm64/include/asm/irqflags.h
> +++ b/arch/arm64/include/asm/irqflags.h
> @@ -18,7 +18,27 @@
>  
>  #ifdef __KERNEL__
>  
> +#include <asm/alternative.h>
> +#include <asm/cpufeature.h>
>  #include <asm/ptrace.h>
> +#include <asm/sysreg.h>
> +
> +
> +/*
> + * When ICC_PMR_EL1 is used for interrupt masking, only the bit indicating
> + * whether the normal interrupts are masked is kept along with the daif
> + * flags.
> + */
> +#define ARCH_FLAG_PMR_EN 0x1
> +
> +#define MAKE_ARCH_FLAGS(daif, pmr)					\
> +	((daif) | (((pmr) >> GIC_PRIO_STATUS_SHIFT) & ARCH_FLAG_PMR_EN))
> +
> +#define ARCH_FLAGS_GET_PMR(flags)				 \
> +	((((flags) & ARCH_FLAG_PMR_EN) << GIC_PRIO_STATUS_SHIFT) \
> +		| GIC_PRIO_IRQOFF)
> +
> +#define ARCH_FLAGS_GET_DAIF(flags) ((flags) & ~ARCH_FLAG_PMR_EN)

I wonder whether we could just use the PSR_I_BIT here to decide whether
to set the GIC_PRIO_IRQ{ON,OFF}. We could clear the PSR_I_BIT in
_restore_daif() with an alternative.

> +/*
> + * CPU interrupt mask handling.
> + */
>  static inline void arch_local_irq_enable(void)
>  {
> -	asm volatile(
> -		"msr	daifclr, #2		// arch_local_irq_enable"
> -		:
> +	unsigned long unmasked = GIC_PRIO_IRQON;
> +
> +	asm volatile(ALTERNATIVE(
> +		"msr	daifclr, #2		// arch_local_irq_enable\n"
> +		"nop",
> +		"msr_s  " __stringify(SYS_ICC_PMR_EL1) ",%0\n"
> +		"dsb	sy",
> +		ARM64_HAS_IRQ_PRIO_MASKING)

DSB needed here as well? I guess I'd have to read the GIC spec before
asking again ;).

-- 
Catalin