Re: [RFC PATCH v2 02/38] KVM: arm/arm64: Enable nested virtualization via command-line

[Christoffer Dall]

On Tue, Jul 18, 2017 at 11:58:28AM -0500, Jintack Lim wrote:
> Add a new kernel parameter(kvm-arm.nested) to enable KVM/ARM nested
> virtualization support. This kernel parameter on arm architecture is
> ignored since nested virtualization is not supported on arm.
> 
> Note that this kernel parameter will not have any impact until nested
> virtualization support is completed. Just add this parameter first to
> use it when implementing nested virtualization support.
> 
> Signed-off-by: Jintack Lim <jintack.lim@xxxxxxxxxx>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  4 ++++
>  arch/arm/include/asm/kvm_host.h                 |  4 ++++
>  arch/arm64/include/asm/kvm_host.h               |  2 ++
>  arch/arm64/kvm/Makefile                         |  2 ++
>  arch/arm64/kvm/nested.c                         | 26 +++++++++++++++++++++++++
>  virt/kvm/arm/arm.c                              |  2 ++
>  6 files changed, 40 insertions(+)
>  create mode 100644 arch/arm64/kvm/nested.c
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index aa8341e..8fb152d 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1841,6 +1841,10 @@
>  			[KVM,ARM] Trap guest accesses to GICv3 common
>  			system registers
>  
> +	kvm-arm.nested=
> +			[KVM,ARM] Allow nested virtualization in KVM/ARM.
> +			Default is 0 (disabled)

We may want to say "on systems that support it" or something like that
here as well.

> +
>  	kvm-intel.ept=	[KVM,Intel] Disable extended page tables
>  			(virtualized MMU) support on capable Intel chips.
>  			Default is 1 (enabled)
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 127e2dd..00b0f97 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -299,4 +299,8 @@ int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,
>  int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
>  			       struct kvm_device_attr *attr);
>  
> +static inline int __init kvmarm_nested_cfg(char *buf)
> +{
> +	return 0;
> +}
>  #endif /* __ARM_KVM_HOST_H__ */
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 0c4fd1f..dcc4df8 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -386,4 +386,6 @@ static inline void __cpu_init_stage2(void)
>  		  "PARange is %d bits, unsupported configuration!", parange);
>  }
>  
> +int __init kvmarm_nested_cfg(char *buf);
> +
>  #endif /* __ARM64_KVM_HOST_H__ */
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 5d98100..f513047 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -35,3 +35,5 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic/vgic-debug.o
>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/irqchip.o
>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arch_timer.o
>  kvm-$(CONFIG_KVM_ARM_PMU) += $(KVM)/arm/pmu.o
> +
> +kvm-$(CONFIG_KVM_ARM_HOST) += nested.o
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> new file mode 100644
> index 0000000..79f38da
> --- /dev/null
> +++ b/arch/arm64/kvm/nested.c
> @@ -0,0 +1,26 @@
> +/*
> + * Copyright (C) 2017 - Columbia University and Linaro Ltd.
> + * Author: Jintack Lim <jintack.lim@xxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/kvm.h>
> +#include <linux/kvm_host.h>
> +
> +static bool nested_param;
> +
> +int __init kvmarm_nested_cfg(char *buf)
> +{
> +	return strtobool(buf, &nested_param);
> +}
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index a39a1e1..1c1c772 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -67,6 +67,8 @@
>  
>  static DEFINE_PER_CPU(unsigned char, kvm_arm_hardware_enabled);
>  
> +early_param("kvm-arm.nested", kvmarm_nested_cfg);
> +
>  static void kvm_arm_set_running_vcpu(struct kvm_vcpu *vcpu)
>  {
>  	BUG_ON(preemptible());
> -- 
> 1.9.1
>