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Date:   Wed, 11 Aug 2021 19:31:36 +0100
Message-ID: <87fsvfal4n.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Chen-Yu Tsai <wenst@chromium.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Alexandru Elisei <Alexandru.Elisei@arm.com>
Subject: Re: [PATCH] irqchip/gic-v3: Fix priority comparison when non-secure priorities are used
In-Reply-To: <20210811171505.1502090-1-wenst@chromium.org>
References: <20210811171505.1502090-1-wenst@chromium.org>
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+ Alex, who introduced this.

On Wed, 11 Aug 2021 18:15:05 +0100,
Chen-Yu Tsai <wenst@chromium.org> wrote:
> 
> When non-secure priorities are used, compared to the raw priority set,
> the value read back from RPR is also right-shifted by one and the
> highest bit set.
> 
> Add a macro to do the modifications to the raw priority when doing the
> comparison against the RPR value. This corrects the pseudo-NMI behavior
> when non-secure priorities in the GIC are used. Tested on 5.10 with
> the "IPI as pseudo-NMI" series [1] applied on MT8195.
> 
> [1] https://lore.kernel.org/linux-arm-kernel/1604317487-14543-1-git-send-email-sumit.garg@linaro.org/
> 
> Fixes: 336780590990 ("irqchip/gic-v3: Support pseudo-NMIs when SCR_EL3.FIQ == 0")
> Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
> ---
>  drivers/irqchip/irq-gic-v3.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index e0f4debe64e1..e7a0b55413db 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -100,6 +100,15 @@ EXPORT_SYMBOL(gic_pmr_sync);
>  DEFINE_STATIC_KEY_FALSE(gic_nonsecure_priorities);
>  EXPORT_SYMBOL(gic_nonsecure_priorities);
>  
> +#define GICD_INT_RPR_PRI(priority)					\
> +	({								\
> +		u32 __priority = (priority);				\
> +		if (static_branch_unlikely(&gic_nonsecure_priorities))	\
> +			__priority = 0x80 | (__priority >> 1);		\
> +									\
> +		__priority;						\

This doesn't reflect what the pseudocode says of a read of ICC_RPR_EL1
AFAICS. When the priority is activated, it is indeed shifted. But a
read of RPR does appear to shift things back (and you loose the lowest
bit in the process). Please see 'aarch64/support/ICC_RPR_EL1' in the
architecture spec.

Can you confirm that SCR_EL3.FIQ is set on your system?

Thanks,

	M.

> +	})
> +
>  /* ppi_nmi_refs[n] == number of cpus having ppi[n + 16] set as NMI */
>  static refcount_t *ppi_nmi_refs;
>  
> @@ -687,7 +696,7 @@ static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs
>  		return;
>  
>  	if (gic_supports_nmi() &&
> -	    unlikely(gic_read_rpr() == GICD_INT_NMI_PRI)) {
> +	    unlikely(gic_read_rpr() == GICD_INT_RPR_PRI(GICD_INT_NMI_PRI))) {
>  		gic_handle_nmi(irqnr, regs);
>  		return;
>  	}


-- 
Without deviation from the norm, progress is not possible.