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

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Date:   Thu, 12 Oct 2017 15:38:51 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 12/10/17 10:22, Thomas Gleixner wrote:
> 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.

I had a look at that initially, and can't remember what I discounted
it... This is obviously a much simpler approach (just an additional flag
as we initialize the vcpus).

I'll drop that patch and post another one.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...