Hi Marc,
On Mon, Nov 29, 2021 at 08:00:48PM +0000, Marc Zyngier wrote:
> From: Christoffer Dall <christoffer.dall@xxxxxxx>
>
> 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@xxxxxxx>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> 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));
kvm_vcpu_init_nested() checks the ARM64_HAS_NESTED_VIRT cap before setting
the features bit, so I guess you can drop this check here if you're
interested in correctness.
But the reason the cap check done is performance, right? Same with the NVHE
define.
Thanks,
Alex
> +}
> +
> +#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;
> --
> 2.30.2
>
