linux-kernel - Re: [PATCH v6 06/24] arm64: ptrace: Provide definitions for PMR values

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Date:   Thu, 29 Nov 2018 16:40:13 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Julien Thierry <julien.thierry@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        daniel.thompson@...aro.org, joel@...lfernandes.org,
        marc.zyngier@....com, christoffer.dall@....com,
        james.morse@....com, catalin.marinas@....com, will.deacon@....com,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v6 06/24] arm64: ptrace: Provide definitions for PMR
 values

On Mon, Nov 12, 2018 at 11:56:57AM +0000, Julien Thierry wrote:
> Introduce fixed values for PMR that are going to be used to mask and
> unmask interrupts by priority. These values are chosent in such a way

Nit: s/chosent/chosen/

> that a single bit (GIC_PMR_UNMASKED_BIT) encodes the information whether
> interrupts are masked or not.

There's no GIC_PMR_UNMASKED_BIT in this patch. Should that be
GIC_PRIO_STATUS_BIT?

> Signed-off-by: Julien Thierry <julien.thierry@....com>
> Suggested-by: Daniel Thompson <daniel.thompson@...aro.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> ---
>  arch/arm64/include/asm/ptrace.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index fce22c4..ce6998c 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -25,6 +25,12 @@
>  #define CurrentEL_EL1		(1 << 2)
>  #define CurrentEL_EL2		(2 << 2)
>  
> +/* PMR values used to mask/unmask interrupts */
> +#define GIC_PRIO_IRQON		0xf0
> +#define GIC_PRIO_STATUS_SHIFT	6
> +#define GIC_PRIO_STATUS_BIT	(1 << GIC_PRIO_STATUS_SHIFT)
> +#define GIC_PRIO_IRQOFF		(GIC_PRIO_IRQON ^ GIC_PRIO_STATUS_BIT)

Could you elaborate on the GIC priority logic a bit?

Are lower numbers higher priority?

Are there restrictions on valid PMR values?

IIUC GIC_PRIO_IRQOFF is 0xb0 (aka 0b10110000), which seems a little
surprising. I'd have expected that we'd use the most signficant bit.


Thanks,
Mark.