Re: [RFC PATCH v2 05/19] KVM: arm/arm64: Check that system supports split eoi/deactivate

Marc Zyngier
2017-08-01T12:37:14Z

On 01/08/17 13:26, Christoffer Dall wrote:
> On Tue, Aug 01, 2017 at 12:35:23PM +0100, Marc Zyngier wrote:
>> On 17/07/17 15:27, Christoffer Dall wrote:
>>> Some systems without proper firmware and/or hardware description data
>>> don't support the split EOI and deactivate operation.
>>>
>>> On such systems, we cannot leave the physical interrupt active after the
>>> timer handler on the host has run, so we cannot support KVM with an
>>> in-kernel GIC with the timer changes we about to introduce.
>>>
>>> This patch makes sure that trying to initialize the KVM GIC code will
>>> fail on such systems.
>>>
>>> Cc: Marc Zyngier <marc.zyngier@arm.com>
>>> Signed-off-by: Christoffer Dall <cdall@linaro.org>
>>> ---
>>> drivers/irqchip/irq-gic.c | 12 +++++++++---
>>> 1 file changed, 9 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
>>> index 090991f..b7e4fed 100644
>>> --- a/drivers/irqchip/irq-gic.c
>>> +++ b/drivers/irqchip/irq-gic.c
>>> @@ -1391,7 +1391,8 @@ int gic_of_init_child(struct device *dev, struct gic_chip_data **gic, int irq)
>>> return 0;
>>> }
>>>
>>> -static void __init gic_of_setup_kvm_info(struct device_node *node)
>>> +static void __init gic_of_setup_kvm_info(struct device_node *node,
>>> + bool supports_deactivate)
>>
>> Ouch, nasty. This shadows the static key which is also called
>> supports_deactivate...
>>
>
> oh, yeah, that's a trap waiting to happen.
>
>>> {
>>> int ret;
>>> struct resource *vctrl_res = &gic_v2_kvm_info.vctrl;
>>> @@ -1411,6 +1412,9 @@ static void __init gic_of_setup_kvm_info(struct device_node *node)
>>> if (ret)
>>> return;
>>>
>>> + if (!supports_deactivate)
>>> + return;
>>> +
>>> gic_set_kvm_info(&gic_v2_kvm_info);
>>
>> Speaking of which, the static key should already be initialized, so this
>> could actually read:
>>
>> if (static_key_true(&supports_deactivate))
>> gic_set_kvm_info(&gic_v2_kvm_info);
>>
>>> }
>>>
>>> @@ -1419,6 +1423,7 @@ gic_of_init(struct device_node *node, struct device_node *parent)
>>> {
>>> struct gic_chip_data *gic;
>>> int irq, ret;
>>> + bool has_eoimode;
>>>
>>> if (WARN_ON(!node))
>>> return -ENODEV;
>>> @@ -1436,7 +1441,8 @@ gic_of_init(struct device_node *node, struct device_node *parent)
>>> * Disable split EOI/Deactivate if either HYP is not available
>>> * or the CPU interface is too small.
>>> */
>>> - if (gic_cnt == 0 && !gic_check_eoimode(node, &gic->raw_cpu_base))
>>> + has_eoimode = gic_check_eoimode(node, &gic->raw_cpu_base);
>>> + if (gic_cnt == 0 && !has_eoimode)
>>> static_key_slow_dec(&supports_deactivate);
>>>
>>> ret = __gic_init_bases(gic, -1, &node->fwnode);
>>> @@ -1447,7 +1453,7 @@ gic_of_init(struct device_node *node, struct device_node *parent)
>>>
>>> if (!gic_cnt) {
>>> gic_init_physaddr(node);
>>> - gic_of_setup_kvm_info(node);
>>> + gic_of_setup_kvm_info(node, has_eoimode);
>>> }
>>>
>>> if (parent) {
>>>
>>
>> and we shouldn't need any of this. What do you think?
>>
>
> I wasn't exactly sure if gic_cnt > 0 && !gic_check_eiomode() could then
> end up registering the KVM info when we shouldn't.
>
> If that's not a concern, I'm happy to rework this.

I think it should be fine. gic_cnt is incremented each time we find a
GIC, and we'll only register the KVM info when we discover the first one
(while gic_cnt is still zero).

Also, nobody is mad enough to have multiple GICs these days (cough...).

Thanks,

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