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

[Christoffer Dall <cdall@linaro.org>]

On Tue, Aug 01, 2017 at 01:37:14PM +0100, Marc Zyngier wrote:
> 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...).
> 

ok, I'll rework it then.

Thanks,
-Christoffer