linux-kernel - Re: [PATCH v4 08/20] irqchip/gic-v4.1: Plumb get/set_irqchip

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Date:   Fri, 28 Feb 2020 19:37:48 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Zenghui Yu <yuzenghui@...wei.com>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jason Cooper <jason@...edaemon.net>,
        Robert Richter <rrichter@...vell.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Auger <eric.auger@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: Re: [PATCH v4 08/20] irqchip/gic-v4.1: Plumb get/set_irqchip_state
 SGI callbacks

On 2020-02-20 03:11, Zenghui Yu wrote:
> Hi Marc,
> 
> On 2020/2/18 23:31, Marc Zyngier wrote:
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c 
>> b/drivers/irqchip/irq-gic-v3-its.c
>> index 7656b353a95f..0ed286dba827 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -144,7 +144,7 @@ struct event_lpi_map {
>>       u16            *col_map;
>>       irq_hw_number_t        lpi_base;
>>       int            nr_lpis;
>> -    raw_spinlock_t        vlpi_lock;
>> +    raw_spinlock_t        map_lock;
> 
> So we use map_lock to protect both LPI's and VLPI's mapping affinity of
> a device, and use vpe_lock to protect vPE's affinity, OK.
> 
>>       struct its_vm        *vm;
>>       struct its_vlpi_map    *vlpi_maps;
>>       int            nr_vlpis;
>> @@ -240,15 +240,33 @@ static struct its_vlpi_map *get_vlpi_map(struct 
>> irq_data *d)
>>       return NULL;
>>   }
>> 
>> -static int irq_to_cpuid(struct irq_data *d)
>> +static int irq_to_cpuid_lock(struct irq_data *d, unsigned long 
>> *flags)
>>   {
>> -    struct its_device *its_dev = irq_data_get_irq_chip_data(d);
>>       struct its_vlpi_map *map = get_vlpi_map(d);
>> +    int cpu;
>> 
>> -    if (map)
>> -        return map->vpe->col_idx;
>> +    if (map) {
>> +        raw_spin_lock_irqsave(&map->vpe->vpe_lock, *flags);
>> +        cpu = map->vpe->col_idx;
>> +    } else {
>> +        struct its_device *its_dev = irq_data_get_irq_chip_data(d);
>> +        raw_spin_lock_irqsave(&its_dev->event_map.map_lock, *flags);
>> +        cpu = its_dev->event_map.col_map[its_get_event_id(d)];
>> +    }
>> 
>> -    return its_dev->event_map.col_map[its_get_event_id(d)];
>> +    return cpu;
>> +}
> 
> This helper is correct for normal LPIs and VLPIs, but wrong for per-vPE
> IRQ (doorbell) and vSGIs. irq_data_get_irq_chip_data() gets confused by
> both of them.

Yes, I've fixed that in the current state of the tree last week. Do have 
a
look if you can, but it seems to survive on both the model with v4.1 and
my D05.

[...]

>> -        rdbase = per_cpu_ptr(gic_rdists->rdist, 
>> vpe->col_idx)->rd_base;
>> +        cpu = irq_to_cpuid_lock(d, &flags);
>> +        rdbase = per_cpu_ptr(gic_rdists->rdist, cpu)->rd_base;
>>           gic_write_lpir(d->parent_data->hwirq, rdbase + 
>> GICR_INVLPIR);
>>           wait_for_syncr(rdbase);
>> +        irq_to_cpuid_unlock(d, flags);
>>       } else {
>>           its_vpe_send_cmd(vpe, its_send_inv);
>>       }
> 
> Do we really need to grab the vpe_lock for those which are belong to
> the same irqchip with its_vpe_set_affinity()? The IRQ core code should
> already ensure the mutual exclusion among them, wrong?

I've been trying to think about that, but jet-lag keeps getting in the 
way.
I empirically think that you are right, but I need to go and check the 
various
code paths to be sure. Hopefully I'll have a bit more brain space next 
week.

For sure this patch tries to do too many things at once...

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