linux-kernel - Re: [PATCH 10/10] irqchip/gic-v4: Make the doorbells managed affinity interrupts

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Message-ID: <alpine.DEB.2.20.1710121118200.1930@nanos>
Date:   Thu, 12 Oct 2017 11:22:20 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Marc Zyngier <marc.zyngier@....com>
cc:     linux-kernel@...r.kernel.org, Jason Cooper <jason@...edaemon.net>,
        Shanker Donthineni <shankerd@...eaurora.org>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
        Christoffer Dall <cdall@...aro.org>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH 10/10] irqchip/gic-v4: Make the doorbells managed affinity
 interrupts

On Tue, 10 Oct 2017, Marc Zyngier wrote:
>  int its_alloc_vcpu_irqs(struct its_vm *vm)
>  {
>  	int vpe_base_irq, i;
>  
> +	vm->affinity_masks = kzalloc(vm->nr_vpes * sizeof(*vm->affinity_masks),
> +				     GFP_KERNEL);
> +	if (!vm->affinity_masks)
> +		goto err;
> +
> +	for (i = 0; i < vm->nr_vpes; i++) {
> +		if (!alloc_cpumask_var(&vm->affinity_masks[i], GFP_KERNEL))
> +			goto err;
> +
> +		cpumask_copy(vm->affinity_masks[i], cpu_possible_mask);

That looks a bit like abuse of managed interrupts as you don't use any of
the managing parts, i.e. the managed shutdown/startup on cpu hotplug.

You can prevent user space from fiddling with the affinities by flagging
these interrupts with IRQ_NO_BALANCING.

Thanks,

	tglx