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

Christoffer Dall
2017-08-28T18:33:47Z

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.

#bikeshedding

Thanks,
-Christoffer

> +}
> +
> /**
> * vgic_v3_probe - probe for a GICv3 compatible interrupt controller in DT
> * @node: pointer to the DT node
> @@ -485,8 +497,16 @@ int vgic_v3_probe(const struct gic_kvm_info *info)
> kvm_vgic_global_state.can_emulate_gicv2 = false;
> kvm_vgic_global_state.ich_vtr_el2 = ich_vtr_el2;
>
> - /* GICv4 support? */
> + /*
> + * GICv4 support? We need to check on all CPUs in case of some
> + * extremely creative form of big-little brain damage...
> + */
> if (info->has_v4) {
> + int cpu;
> +
> + for_each_online_cpu(cpu)
> + smp_call_function_single(cpu, vgic_check_v4_cpuif,
> + &gicv4_enable, 1);
> kvm_vgic_global_state.has_gicv4 = gicv4_enable;
> kvm_info("GICv4 support %sabled\n",
> gicv4_enable ? "en" : "dis");
> --
> 2.11.0
>