Re: [Qemu-arm] [Qemu-devel] [RFC v2 3/3] virt: Check KVM_CAP_ARM_IRQ_LINE_LAYOUT_2 for smp_cpus > 256

[Andrew Jones]

On Wed, Sep 11, 2019 at 05:51:25PM +0200, Eric Auger wrote:
> Host kernel within [4.18, 5.3] report an erroneous KVM_MAX_VCPUS=512
> for ARM. The actual capability to instantiate more than 256 vcpus
> was fixed in 5.4 with the upgrade of the KVM_IRQ_LINE ABI to support
> vcpu id encoded on 12 bits instead of 8 and a redistributor consuming
> a single KVM IO device instead of 2.
> 
> So let's check this capability when attempting to use more than 256
> vcpus.
> 
> Signed-off-by: Eric Auger <address@hidden>
> ---
>  hw/arm/virt.c        |  4 ++++
>  target/arm/kvm.c     | 21 +++++++++++++++++++++
>  target/arm/kvm_arm.h | 15 +++++++++++++++
>  3 files changed, 40 insertions(+)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 0d1629ccb3..465e3140f7 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1575,6 +1575,10 @@ static void machvirt_init(MachineState *machine)
>          virt_max_cpus = GIC_NCPU;
>      }
>  
> +    if (kvm_arm_irq_line_layout_mismatch(MACHINE(vms), max_cpus)) {
> +        exit(1);
> +    }
> +
>      if (max_cpus > virt_max_cpus) {
>          error_report("Number of SMP CPUs requested (%d) exceeds max CPUs "
>                       "supported by machine 'mach-virt' (%d)",
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index 6cdfa2204f..b601e2f35a 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -171,6 +171,27 @@ bool kvm_arm_pmu_supported(CPUState *cpu)
>      return kvm_check_extension(s, KVM_CAP_ARM_PMU_V3);
>  }
>  
> +bool kvm_arm_irq_line_layout_mismatch(MachineState *ms, int vcpus)
> +{
> +    KVMState *s;
> +    bool ret;
> +
> +    if (!kvm_enabled()) {
> +        return false;
> +    }
> +
> +    s = KVM_STATE(ms->accelerator);
> +
> +    ret = vcpus > 256 &&
> +          !kvm_check_extension(s, KVM_CAP_ARM_IRQ_LINE_LAYOUT_2);
> +
> +    if (ret) {
> +        error_report("Using more than 256 vcpus requires a host kernel "
> +                     "with KVM_CAP_ARM_IRQ_LINE_LAYOUT_2");
> +    }
> +    return ret;
> +}
> +
>  int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
>  {
>      KVMState *s = KVM_STATE(ms->accelerator);
> diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> index b4e19457a0..d893d950d8 100644
> --- a/target/arm/kvm_arm.h
> +++ b/target/arm/kvm_arm.h
> @@ -233,6 +233,16 @@ bool kvm_arm_pmu_supported(CPUState *cs);
>   */
>  int kvm_arm_get_max_vm_ipa_size(MachineState *ms);
>  
> +/**
> + * kvm_arm_irq_line_layout_mismatch - Returns whether the number of vcpus
> + * exceeds the limit imposed by the legacy KVM_IRQ_LINE ARM layout
> + * (without the vcpu2_index field).
> + *
> + * @ms: Machine state handle
> + * @vcpus: number of vcpus
> + */
> +bool kvm_arm_irq_line_layout_mismatch(MachineState *ms, int vcpus);
> +
>  /**
>   * kvm_arm_sync_mpstate_to_kvm
>   * @cpu: ARMCPU
> @@ -281,6 +291,11 @@ static inline int 
> kvm_arm_get_max_vm_ipa_size(MachineState *ms)
>      return -ENOENT;
>  }
>  
> +static inline bool kvm_arm_irq_line_layout_mismatch(MachineState *ms, int 
> vcpus)
> +{
> +    return false;
> +}
> +
>  static inline int kvm_arm_vgic_probe(void)
>  {
>      return 0;
> -- 
> 2.20.1
> 
>

Reviewed-by: Andrew Jones <address@hidden>