linux-kernel - Re: [PATCH] irqchip/gic-v3-its: Flush GICR caching for a cross node collection move of an irq

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Date:   Wed, 20 Dec 2017 15:04:52 +0530
From:   Ganapatrao Kulkarni <gklkml16@...il.com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Thomas Gleixner <tglx@...utronix.de>, jason@...edaemon.net,
        catalin.marinas@....com, Will Deacon <will.deacon@....com>,
        jnair@...iumnetworks.com,
        Robert Richter <Robert.Richter@...ium.com>,
        Jan.Glauber@...ium.com
Subject: Re: [PATCH] irqchip/gic-v3-its: Flush GICR caching for a cross node
 collection move of an irq

Hi Marc,

On Wed, Dec 20, 2017 at 2:56 PM, Marc Zyngier <marc.zyngier@....com> wrote:
> On 20/12/17 09:15, Ganapatrao Kulkarni wrote:
>> When an interrupt is moved, it is possible that an implementation that
>> supports caching might still have cached data for a previous
>> (no longer valid) mapping of the interrupt. In particular, in a distributed
>> GIC implementation like multi-socket SoC platfroms. Hence it is necessary
>> to flush cached entries after cross node collection migration.
>>
>> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
>> ---
>>  drivers/irqchip/irq-gic-v3-its.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 4039e64..ea849a1 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -1119,6 +1119,12 @@ static int its_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
>>       if (cpu != its_dev->event_map.col_map[id]) {
>>               target_col = &its_dev->its->collections[cpu];
>>               its_send_movi(its_dev, target_col, id);
>> +             /* Issue INV for cross node collection move on
>> +              * multi socket systems.
>> +              */
>> +             if (cpu_to_node(cpu) !=
>> +                             cpu_to_node(its_dev->event_map.col_map[id]))
>> +                     its_send_inv(its_dev, id);
>>               its_dev->event_map.col_map[id] = cpu;
>>               irq_data_update_effective_affinity(d, cpumask_of(cpu));
>>       }
>>
>
> The MOVI command doesn't have any such requirement (it only mandates
> synchronization), and doesn't say anything about distributed vs monolithic.

GIC-v3 spec do mention to issue ITS INV command or a write to GICR_INVLPIR.
pasting below snippet of MOVI command description.

"When an interrupt is moved to a collection, it is possible that an
implementation that supports speculative caching
might still have cached data for a previous (no longer valid) mapping
of the interrupt. Hence, implementations
must take care to invalidate any data associated with an interrupt
when it is moved. In particular, in a distributed
implementation, the ITS must write to the appropriate GICR_* register
to perform the invalidation in the redistributor."

>
> What am I missing?
>
>         M.
> --
> Jazz is not dead. It just smells funny...

thanks
Ganapat