[PATCH v5 07/69] KVM: arm64: nv: Introduce nested virtualization VCPU feature

[Ganapatrao Kulkarni]

Hi Marc,

On 30-11-2021 01:30 am, Marc Zyngier wrote:
> From: Christoffer Dall <christoffer.dall at arm.com>
> 
> Introduce the feature bit and a primitive that checks if the feature is
> set behind a static key check based on the cpus_have_const_cap check.
> 
> Checking nested_virt_in_use() on systems without nested virt enabled
> should have neglgible overhead.

Typo: negligible

> 
> We don't yet allow userspace to actually set this feature.
> 
> Signed-off-by: Christoffer Dall <christoffer.dall at arm.com>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>   arch/arm64/include/asm/kvm_nested.h | 14 ++++++++++++++
>   arch/arm64/include/uapi/asm/kvm.h   |  1 +
>   2 files changed, 15 insertions(+)
>   create mode 100644 arch/arm64/include/asm/kvm_nested.h
> 
> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
> new file mode 100644
> index 000000000000..1028ac65a897
> --- /dev/null
> +++ b/arch/arm64/include/asm/kvm_nested.h
> @@ -0,0 +1,14 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ARM64_KVM_NESTED_H
> +#define __ARM64_KVM_NESTED_H
> +
> +#include <linux/kvm_host.h>
> +
> +static inline bool nested_virt_in_use(const struct kvm_vcpu *vcpu)
> +{
> +	return (!__is_defined(__KVM_NVHE_HYPERVISOR__) &&
> +		cpus_have_final_cap(ARM64_HAS_NESTED_VIRT) &&
> +		test_bit(KVM_ARM_VCPU_HAS_EL2, vcpu->arch.features));
> +}
> +
> +#endif /* __ARM64_KVM_NESTED_H */
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index b3edde68bc3e..395a4c039bcc 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -106,6 +106,7 @@ struct kvm_regs {
>   #define KVM_ARM_VCPU_SVE		4 /* enable SVE for this CPU */
>   #define KVM_ARM_VCPU_PTRAUTH_ADDRESS	5 /* VCPU uses address authentication */
>   #define KVM_ARM_VCPU_PTRAUTH_GENERIC	6 /* VCPU uses generic authentication */
> +#define KVM_ARM_VCPU_HAS_EL2		7 /* Support nested virtualization */
>   
>   struct kvm_vcpu_init {
>   	__u32 target;

It looks good to me.
Please feel free to add.
Reviewed-by: Ganapatrao Kulkarni <gankulkarni at os.amperecomputing.com>

Thanks,
Ganapat