linux-kernel - Re: [PATCH] irqchip/gic-v4.1: Ensure accessing the correct RD when writing INVALLR

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Date:   Fri, 17 Jul 2020 12:07:56 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Zenghui Yu <yuzenghui@...wei.com>
Cc:     <linux-kernel@...r.kernel.org>, <tglx@...utronix.de>,
        <jason@...edaemon.net>, <wanghaibin.wang@...wei.com>
Subject: Re: [PATCH] irqchip/gic-v4.1: Ensure accessing the correct RD when writing INVALLR

On Thu, 09 Jul 2020 14:49:59 +0100,
Zenghui Yu <yuzenghui@...wei.com> wrote:
> 
> The GICv4.1 spec tells us that it's CONSTRAINED UNPREDICTABLE to issue a
> register-based invalidation operation for a vPEID not mapped to that RD,
> or another RD within the same CommonLPIAff group.
> 
> To follow this rule, commit f3a059219bc7 ("irqchip/gic-v4.1: Ensure mutual
> exclusion between vPE affinity change and RD access") tried to address the
> race between the RD accesses and the vPE affinity change, but somehow
> forgot to take GICR_INVALLR into account. Let's take the vpe_lock before
> evaluating vpe->col_idx to fix it.
> 
> Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>

Shouldn't this deserve a Fixes: tag?

Thanks,

	M.

> ---
>  drivers/irqchip/irq-gic-v3-its.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index da44bfa48bc2..50a04cca8207 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -4087,18 +4087,22 @@ static void its_vpe_4_1_deschedule(struct its_vpe *vpe,
>  static void its_vpe_4_1_invall(struct its_vpe *vpe)
>  {
>  	void __iomem *rdbase;
> +	unsigned long flags;
>  	u64 val;
> +	int cpu;
>  
>  	val  = GICR_INVALLR_V;
>  	val |= FIELD_PREP(GICR_INVALLR_VPEID, vpe->vpe_id);
>  
>  	/* Target the redistributor this vPE is currently known on */
> -	raw_spin_lock(&gic_data_rdist_cpu(vpe->col_idx)->rd_lock);
> -	rdbase = per_cpu_ptr(gic_rdists->rdist, vpe->col_idx)->rd_base;
> +	cpu = vpe_to_cpuid_lock(vpe, &flags);
> +	raw_spin_lock(&gic_data_rdist_cpu(cpu)->rd_lock);
> +	rdbase = per_cpu_ptr(gic_rdists->rdist, cpu)->rd_base;
>  	gic_write_lpir(val, rdbase + GICR_INVALLR);
>  
>  	wait_for_syncr(rdbase);
> -	raw_spin_unlock(&gic_data_rdist_cpu(vpe->col_idx)->rd_lock);
> +	raw_spin_unlock(&gic_data_rdist_cpu(cpu)->rd_lock);
> +	vpe_to_cpuid_unlock(vpe, flags);
>  }
>  
>  static int its_vpe_4_1_set_vcpu_affinity(struct irq_data *d, void *vcpu_info)
> -- 
> 2.19.1
> 
> 

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