Re: [PATCH v3 56/59] KVM: arm/arm64: GICv4: Prevent heterogenous systems from using GICv4

Marc Zyngier
2017-08-30T16:03:51Z

On 28/08/17 19:35, Christoffer Dall wrote:
> On Mon, Jul 31, 2017 at 06:26:34PM +0100, Marc Zyngier wrote:
>> The GICv4 architecture doesn't prevent CPUs implementing GICv4 to
>> cohabit with CPUs limited to GICv3 in the same system.
>>
>> This is mad (the sheduler would have to be made aware of the v4
>
> *scheduler
>
>> capability), and we're certainly not going to support this any
>> time soon. So let's check that all online CPUs are GICv4 capable,
>> and disable the functionnality if not.
>
> *functionality
>
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>> include/linux/irqchip/arm-gic-v3.h | 2 ++
>> virt/kvm/arm/vgic/vgic-v3.c | 22 +++++++++++++++++++++-
>> 2 files changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
>> index 1ea576c8126f..dfa4a51643d6 100644
>> --- a/include/linux/irqchip/arm-gic-v3.h
>> +++ b/include/linux/irqchip/arm-gic-v3.h
>> @@ -532,6 +532,8 @@
>> #define ICH_VTR_SEIS_MASK (1 << ICH_VTR_SEIS_SHIFT)
>> #define ICH_VTR_A3V_SHIFT 21
>> #define ICH_VTR_A3V_MASK (1 << ICH_VTR_A3V_SHIFT)
>> +#define ICH_VTR_nV4_SHIFT 20
>> +#define ICH_VTR_nV4_MASK (1 << ICH_VTR_nV4_SHIFT)
>>
>> #define ICC_IAR1_EL1_SPURIOUS 0x3ff
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
>> index 405733678c2f..252268e83ade 100644
>> --- a/virt/kvm/arm/vgic/vgic-v3.c
>> +++ b/virt/kvm/arm/vgic/vgic-v3.c
>> @@ -466,6 +466,18 @@ static int __init early_gicv4_enable(char *buf)
>> }
>> early_param("kvm-arm.vgic_v4_enable", early_gicv4_enable);
>>
>> +static void vgic_check_v4_cpuif(void *param)
>> +{
>> + u32 ich_vtr_el2 = kvm_call_hyp(__vgic_v3_get_ich_vtr_el2);
>> + bool *v4 = param, this_cpu_is_v4;
>> +
>> + this_cpu_is_v4 = !(ich_vtr_el2 & ICH_VTR_nV4_MASK);
>> + if (!this_cpu_is_v4)
>> + kvm_info("CPU%d is not GICv4 capable\n", smp_processor_id());
>> +
>> + *v4 &= this_cpu_is_v4;
>
> nit: You could make this function look slightly less scary by declaring
> this_cpu_is_v4 on a separate line and not use a bitwise operator on a
> boolean type. Actually, having a function called 'check' with a side
> effect is not the nicest thing either, so why not just return what this
> particular CPU does and do the comparison in the calling loop.

Fair enough.

> #bikeshedding

How about this on top:

diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
index 01eaf4ee2f63..e471750dc0a1 100644
--- a/virt/kvm/arm/vgic/vgic-v3.c
+++ b/virt/kvm/arm/vgic/vgic-v3.c
@@ -469,18 +469,16 @@ early_param("kvm-arm.vgic_v4_enable", early_gicv4_enable);
static void vgic_check_v4_cpuif(void *param)
{
u32 ich_vtr_el2 = kvm_call_hyp(__vgic_v3_get_ich_vtr_el2);
- bool *v4 = param, this_cpu_is_v4;
+ bool *v4 = param;

- this_cpu_is_v4 = !(ich_vtr_el2 & ICH_VTR_nV4_MASK);
- if (!this_cpu_is_v4)
+ *v4 = !(ich_vtr_el2 & ICH_VTR_nV4_MASK);
+ if (!*v4)
kvm_info("CPU%d is not GICv4 capable\n", smp_processor_id());
-
- *v4 &= this_cpu_is_v4;
}

/**
* vgic_v3_probe - probe for a GICv3 compatible interrupt controller in DT
- * @node: pointer to the DT node
+ * @info: pointer to the firmware-agnostic GIC information
*
* Returns 0 if a GICv3 has been found, returns an error code otherwise
*/
@@ -504,9 +502,14 @@ int vgic_v3_probe(const struct gic_kvm_info *info)
if (info->has_v4) {
int cpu;

- for_each_online_cpu(cpu)
+ for_each_online_cpu(cpu) {
+ bool enable;
+
smp_call_function_single(cpu, vgic_check_v4_cpuif,
- &gicv4_enable, 1);
+ &enable, 1);
+ gicv4_enable = gicv4_enable && enable;
+ }
+
kvm_vgic_global_state.has_gicv4 = gicv4_enable;
kvm_info("GICv4 support %sabled\n",
gicv4_enable ? "en" : "dis");

Thanks,

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