Re: [PATCH v3 30/36] KVM: arm64: Allow userspace to create protected VMs when pKVM is enabled

Fuad Tabba
2026-03-11T10:25:58Z

On Thu, 5 Mar 2026 at 14:45, Will Deacon <will@kernel.org> wrote:
>
> Introduce a new VM type for KVM/arm64 to allow userspace to request the
> creation of a "protected VM" when the host has booted with pKVM enabled.
>
> For now, this depends on CONFIG_EXPERT and results in a taint on first
> use as many aspects of a protected VM are not yet protected!
>
> Signed-off-by: Will Deacon <will@kernel.org>

Reviewed-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad

> ---
> arch/arm64/include/asm/kvm_pkvm.h | 2 +-
> arch/arm64/kvm/Kconfig | 10 ++++++++++
> arch/arm64/kvm/arm.c | 8 +++++++-
> arch/arm64/kvm/mmu.c | 3 ---
> arch/arm64/kvm/pkvm.c | 11 ++++++++++-
> include/uapi/linux/kvm.h | 5 +++++
> 6 files changed, 33 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
> index 7041e398fb4c..2954b311128c 100644
> --- a/arch/arm64/include/asm/kvm_pkvm.h
> +++ b/arch/arm64/include/asm/kvm_pkvm.h
> @@ -17,7 +17,7 @@
>
> #define HYP_MEMBLOCK_REGIONS 128
>
> -int pkvm_init_host_vm(struct kvm *kvm);
> +int pkvm_init_host_vm(struct kvm *kvm, unsigned long type);
> int pkvm_create_hyp_vm(struct kvm *kvm);
> bool pkvm_hyp_vm_is_created(struct kvm *kvm);
> void pkvm_destroy_hyp_vm(struct kvm *kvm);
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 7d1f22fd490b..e71f7fb6e89a 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -82,4 +82,14 @@ config PTDUMP_STAGE2_DEBUGFS
>
> If in doubt, say N.
>
> +config PROTECTED_VM_UAPI
> + bool "Expose protected VMs to userspace (experimental)"
> + depends on KVM && EXPERT
> + help
> + Say Y here to enable experimental (i.e. in development)
> + support for creating protected virtual machines using KVM's
> + KVM_CREATE_VM ioctl() when booted with pKVM enabled.
> +
> + Unless you are a KVM developer, say N.
> +
> endif # VIRTUALIZATION
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 3589fc08266c..c2b666a46893 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -203,6 +203,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> {
> int ret;
>
> + if (type & ~KVM_VM_TYPE_ARM_MASK)
> + return -EINVAL;
> +
> mutex_init(&kvm->arch.config_lock);
>
> #ifdef CONFIG_LOCKDEP
> @@ -234,9 +237,12 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> * If any failures occur after this is successful, make sure to
> * call __pkvm_unreserve_vm to unreserve the VM in hyp.
> */
> - ret = pkvm_init_host_vm(kvm);
> + ret = pkvm_init_host_vm(kvm, type);
> if (ret)
> goto err_uninit_mmu;
> + } else if (type & KVM_VM_TYPE_ARM_PROTECTED) {
> + ret = -EINVAL;
> + goto err_uninit_mmu;
> }
>
> kvm_vgic_early_init(kvm);
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 4e64528d86a6..7655e4c61c4e 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -881,9 +881,6 @@ static int kvm_init_ipa_range(struct kvm_s2_mmu *mmu, unsigned long type)
> u64 mmfr0, mmfr1;
> u32 phys_shift;
>
> - if (type & ~KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
> - return -EINVAL;
> -
> phys_shift = KVM_VM_TYPE_ARM_IPA_SIZE(type);
> if (is_protected_kvm_enabled()) {
> phys_shift = kvm_ipa_limit;
> diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
> index da0a45dab203..d1eb6e23367e 100644
> --- a/arch/arm64/kvm/pkvm.c
> +++ b/arch/arm64/kvm/pkvm.c
> @@ -219,9 +219,13 @@ void pkvm_destroy_hyp_vm(struct kvm *kvm)
> mutex_unlock(&kvm->arch.config_lock);
> }
>
> -int pkvm_init_host_vm(struct kvm *kvm)
> +int pkvm_init_host_vm(struct kvm *kvm, unsigned long type)
> {
> int ret;
> + bool protected = type & KVM_VM_TYPE_ARM_PROTECTED;
> +
> + if (protected && !IS_ENABLED(CONFIG_PROTECTED_VM_UAPI))
> + return -EINVAL;
>
> if (pkvm_hyp_vm_is_created(kvm))
> return -EINVAL;
> @@ -236,6 +240,11 @@ int pkvm_init_host_vm(struct kvm *kvm)
> return ret;
>
> kvm->arch.pkvm.handle = ret;
> + kvm->arch.pkvm.is_protected = protected;
> + if (protected) {
> + pr_warn_once("kvm: protected VMs are for development only, tainting kernel\n");
> + add_taint(TAINT_USER, LOCKDEP_STILL_OK);
> + }
>
> return 0;
> }
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 65500f5db379..50348efe3384 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -699,6 +699,11 @@ struct kvm_enable_cap {
> #define KVM_VM_TYPE_ARM_IPA_SIZE_MASK 0xffULL
> #define KVM_VM_TYPE_ARM_IPA_SIZE(x) \
> ((x) & KVM_VM_TYPE_ARM_IPA_SIZE_MASK)
> +
> +#define KVM_VM_TYPE_ARM_PROTECTED (1UL << 31)
> +#define KVM_VM_TYPE_ARM_MASK (KVM_VM_TYPE_ARM_IPA_SIZE_MASK | \
> + KVM_VM_TYPE_ARM_PROTECTED)
> +
> /*
> * ioctls for /dev/kvm fds:
> */
> --
> 2.53.0.473.g4a7958ca14-goog
>