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

Christoffer Dall
2017-08-30T20:58:16Z

On Wed, Aug 30, 2017 at 05:03:51PM +0100, Marc Zyngier wrote:
> 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");
>

Looks good to me, thanks!
-Christoffer