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

Julien Thierry
2019-06-21T13:08:33Z

On 21/06/2019 10:37, 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>
> ---
> arch/arm/include/asm/kvm_nested.h | 9 +++++++++
> arch/arm64/include/asm/kvm_nested.h | 13 +++++++++++++
> arch/arm64/include/uapi/asm/kvm.h | 1 +
> 3 files changed, 23 insertions(+)
> create mode 100644 arch/arm/include/asm/kvm_nested.h
> create mode 100644 arch/arm64/include/asm/kvm_nested.h
>
> diff --git a/arch/arm/include/asm/kvm_nested.h b/arch/arm/include/asm/kvm_nested.h
> new file mode 100644
> index 000000000000..124ff6445f8f
> --- /dev/null
> +++ b/arch/arm/include/asm/kvm_nested.h
> @@ -0,0 +1,9 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ARM_KVM_NESTED_H
> +#define __ARM_KVM_NESTED_H
> +
> +#include <linux/kvm_host.h>
> +
> +static inline bool nested_virt_in_use(const struct kvm_vcpu *vcpu) { return false; }
> +
> +#endif /* __ARM_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..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);

Nit: You could make it even cheaper for some systems by adding
IS_DEFINED(CONFIG_ARM64_VHE). It would also make the dependency between
NV and VHE more explicit.

Otherwise:

Reviewed-by: Julien Thierry <julien.thierry@arm.com>

Cheers,

--
Julien Thierry