Subject: Re: [PATCH v3 33/33] KVM: PPC: Book3S HV: Add a VM capability to enable nested virtualization

From: David Gibson <[email-masked]>
Date: Wed, 3 Oct 2018 16:21:44 +1000

On Tue, Oct 02, 2018 at 09:31:32PM +1000, Paul Mackerras wrote:
> With this, userspace can enable a KVM-HV guest to run nested guests
> under it.
> 
> Signed-off-by: Paul Mackerras <[email-masked]>
> ---
>  Documentation/virtual/kvm/api.txt  | 14 ++++++++++++++
>  arch/powerpc/include/asm/kvm_ppc.h |  1 +
>  arch/powerpc/kvm/book3s_hv.c       | 17 +++++++++++++++++
>  arch/powerpc/kvm/powerpc.c         | 12 ++++++++++++
>  include/uapi/linux/kvm.h           |  1 +
>  5 files changed, 45 insertions(+)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 017d851..a2d4832 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -4522,6 +4522,20 @@ hpage module parameter is not set to 1, -EINVAL is returned.
>  While it is generally possible to create a huge page backed VM without
>  this capability, the VM will not be able to run.
>  
> +7.15 KVM_CAP_PPC_NESTED_HV
> +
> +Architectures: ppc
> +Parameters: enable flag (0 to disable, non-zero to enable)
> +Returns: 0 on success, -EINVAL when the implementation doesn't support
> +nested-HV virtualization.
> +
> +HV-KVM on POWER9 and later systems allows for "nested-HV"
> +virtualization, which provides a way for a guest VM to run guests that
> +can run using the CPU's supervisor mode (privileged non-hypervisor
> +state).  Enabling this capability on a VM depends on the CPU having
> +the necessary functionality and on the facility being enabled with a
> +kvm-hv module parameter.
> +
>  8. Other capabilities.
>  ----------------------
>  
> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> index 245e564..80f0091 100644
> --- a/arch/powerpc/include/asm/kvm_ppc.h
> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> @@ -327,6 +327,7 @@ struct kvmppc_ops {
>  	int (*set_smt_mode)(struct kvm *kvm, unsigned long mode,
>  			    unsigned long flags);
>  	void (*giveup_ext)(struct kvm_vcpu *vcpu, ulong msr);
> +	int (*enable_nested)(struct kvm *kvm, bool enable);
>  };
>  
>  extern struct kvmppc_ops *kvmppc_hv_ops;
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 196bff1..a5b3862 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -118,6 +118,11 @@ module_param_cb(h_ipi_redirect, &module_param_ops, &h_ipi_redirect, 0644);
>  MODULE_PARM_DESC(h_ipi_redirect, "Redirect H_IPI wakeup to a free host core");
>  #endif
>  
> +/* If set, guests are allowed to create and control nested guests */
> +static bool enable_nested = true;
> +module_param(enable_nested, bool, S_IRUGO | S_IWUSR);
> +MODULE_PARM_DESC(enable_nested, "Enable nested virtualization (only on POWER9)");

I'd suggest calling the module parameter just "nested" to match x86.

>  /* If set, the threads on each CPU core have to be in the same MMU mode */
>  static bool no_mixing_hpt_and_radix;
>  
> @@ -5188,6 +5193,17 @@ static int kvmhv_configure_mmu(struct kvm *kvm, struct kvm_ppc_mmuv3_cfg *cfg)
>  	return err;
>  }
>  
> +static int kvmhv_enable_nested(struct kvm *kvm, bool enable)
> +{
> +	if (!(enable_nested && cpu_has_feature(CPU_FTR_ARCH_300)))
> +		return -EINVAL;

Maybe EPERM, rather than EINVAL.  There's nothing invalid about the
ioctl() parameters - we just can't do what they want.

> +
> +	/* kvm == NULL means the caller is testing if the capability exists */
> +	if (kvm)
> +		kvm->arch.nested_enable = enable;
> +	return 0;
> +}
> +
>  static struct kvmppc_ops kvm_ops_hv = {
>  	.get_sregs = kvm_arch_vcpu_ioctl_get_sregs_hv,
>  	.set_sregs = kvm_arch_vcpu_ioctl_set_sregs_hv,
> @@ -5227,6 +5243,7 @@ static struct kvmppc_ops kvm_ops_hv = {
>  	.configure_mmu = kvmhv_configure_mmu,
>  	.get_rmmu_info = kvmhv_get_rmmu_info,
>  	.set_smt_mode = kvmhv_set_smt_mode,
> +	.enable_nested = kvmhv_enable_nested,
>  };
>  
>  static int kvm_init_subcore_bitmap(void)
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index eba5756..449ae1d 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -596,6 +596,10 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_PPC_MMU_HASH_V3:
>  		r = !!(hv_enabled && cpu_has_feature(CPU_FTR_ARCH_300));
>  		break;
> +	case KVM_CAP_PPC_NESTED_HV:
> +		r = !!(hv_enabled && kvmppc_hv_ops->enable_nested &&
> +		       !kvmppc_hv_ops->enable_nested(NULL, false));
> +		break;
>  #endif
>  	case KVM_CAP_SYNC_MMU:
>  #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> @@ -2114,6 +2118,14 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  			r = kvm->arch.kvm_ops->set_smt_mode(kvm, mode, flags);
>  		break;
>  	}
> +
> +	case KVM_CAP_PPC_NESTED_HV:
> +		r = -EINVAL;
> +		if (!is_kvmppc_hv_enabled(kvm) ||
> +		    !kvm->arch.kvm_ops->enable_nested)
> +			break;
> +		r = kvm->arch.kvm_ops->enable_nested(kvm, !!cap->args[0]);
> +		break;
>  #endif
>  	default:
>  		r = -EINVAL;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 07548de..a6d5a46 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -952,6 +952,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_S390_HPAGE_1M 156
>  #define KVM_CAP_NESTED_STATE 157
>  #define KVM_CAP_ARM_INJECT_SERROR_ESR 158
> +#define KVM_CAP_PPC_NESTED_HV 160
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson