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

[Marc Zyngier]

On 20/12/17 09:34, Ganapatrao Kulkarni wrote:
> Hi Marc,
> 
> On Wed, Dec 20, 2017 at 2:56 PM, Marc Zyngier <marc.zyngier@xxxxxxx> 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 (no longer valid) mapping of the interrupt.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@xxxxxxxxxx>
>>> ---
>>>  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 might still have cached data for a previous (no longer valid) mapping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."

Which document is that from? The only official document that should be
used is the GICv3/v4 Architecture Specification[1], which doesn't
contain that text.

Thanks,

	M.

[1]:
https://developer.arm.com/products/architecture/a-profile/docs/ihi0069/latest/arm-generic-interrupt-controller-architecture-specification-gic-architecture-version-30-and-40
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