Subject: [PATCH v4 31/38] KVM: arm64: Allow userspace to create protected VMs when pKVM is enabled

From: Will Deacon <[email-masked]>
Date: Fri, 27 Mar 2026 14:00:30 +0000

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 feature results in a taint on first use as many aspects of
a protected VM are not yet protected!

Tested-by: Fuad Tabba <[email-masked]>
Tested-by: Mostafa Saleh <[email-masked]>
Signed-off-by: Will Deacon <[email-masked]>
---
 arch/arm64/include/asm/kvm_pkvm.h | 2 +-
 arch/arm64/kvm/arm.c              | 8 +++++++-
 arch/arm64/kvm/mmu.c              | 3 ---
 arch/arm64/kvm/pkvm.c             | 8 +++++++-
 include/uapi/linux/kvm.h          | 5 +++++
 5 files changed, 20 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/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 6a4151e3e4a3..45358ae8a300 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..632852648012 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -219,9 +219,10 @@ 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 (pkvm_hyp_vm_is_created(kvm))
 		return -EINVAL;
@@ -236,6 +237,11 @@ 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 experimental and 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 80364d4dbebb..073b2bcaf560 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -703,6 +703,11 @@ 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:
  */
-- 
2.53.0.1018.g2bb0e51243-goog