Re: [PATCH v3 06/20] KVM: arm/arm64: Check that system supports split eoi/deactivate

Christoffer Dall
2017-10-18T13:40:43Z

On Mon, Oct 09, 2017 at 05:47:18PM +0100, Marc Zyngier wrote:
> On 23/09/17 01:41, 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 are 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 | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> > index f641e8e..ab12bf4 100644
> > --- a/drivers/irqchip/irq-gic.c
> > +++ b/drivers/irqchip/irq-gic.c
> > @@ -1420,7 +1420,8 @@ static void __init gic_of_setup_kvm_info(struct device_node *node)
> > if (ret)
> > return;
> >
> > - gic_set_kvm_info(&gic_v2_kvm_info);
> > + if (static_key_true(&supports_deactivate))
> > + gic_set_kvm_info(&gic_v2_kvm_info);
> > }
> >
> > int __init
> >
>
> Should we add the same level of checking on the ACPI path, just for the
> sake symmetry?

Yes, we should, if anyone is crazy enough to use ACPI :)

>
> Also, do we need to add the same thing for GICv3?
>

Why would split EOI/deactivate not be available on GICv3, actually? It
looks like this is not supported unless you have EL2, but I can't seem
to find anything in the spec for this, and KVM should support
EOI/deactivate for GICv3 guests I think. Am I missing something?

Assuming I'm wrong about GICv3, which I probably am, how does this look
(on top of the posted patch):

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 519149e..aed524c 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -1228,7 +1228,9 @@ static int __init gic_of_init(struct device_node *node, struct device_node *pare
goto out_unmap_rdist;

gic_populate_ppi_partitions(node);
- gic_of_setup_kvm_info(node);
+
+ if (static_key_true(&supports_deactivate))
+ gic_of_setup_kvm_info(node);
return 0;

out_unmap_rdist:
@@ -1517,7 +1519,9 @@ gic_acpi_init(struct acpi_subtable_header *header, const unsigned long end)
goto out_fwhandle_free;

acpi_set_irq_model(ACPI_IRQ_MODEL_GIC, domain_handle);
- gic_acpi_setup_kvm_info();
+
+ if (static_key_true(&supports_deactivate))
+ gic_acpi_setup_kvm_info();

return 0;

diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index ab12bf4..121af5c 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -1653,7 +1653,8 @@ static int __init gic_v2_acpi_init(struct acpi_subtable_header *header,
if (IS_ENABLED(CONFIG_ARM_GIC_V2M))
gicv2m_init(NULL, gic_data[0].domain);

- gic_acpi_setup_kvm_info();
+ if (static_key_true(&supports_deactivate))
+ gic_acpi_setup_kvm_info();

return 0;
}

Thanks,
-Christoffer