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

Will Deacon
2026-03-05T14:45:54Z

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>
---
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