Re: [PATCH 04/59] KVM: arm64: nv: Introduce nested virtualization VCPU feature

Dave Martin
2019-06-24T11:43:38Z

On Fri, Jun 21, 2019 at 10:37:48AM +0100, Marc Zyngier wrote:
> From: Christoffer Dall <christoffer.dall@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.
>
> We don't yet allow userspace to actually set this feature.
>
> Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---

[...]

> diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
> new file mode 100644
> index 000000000000..8a3d121a0b42
> --- /dev/null
> +++ b/arch/arm64/include/asm/kvm_nested.h
> @@ -0,0 +1,13 @@
> +/* 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 cpus_have_const_cap(ARM64_HAS_NESTED_VIRT) &&
> + test_bit(KVM_ARM_VCPU_NESTED_VIRT, vcpu->arch.features);
> +}

Also, is it worth having a vcpu->arch.flags flag for this, similarly to
SVE and ptrauth?

[...]

Cheers
---Dave