[v8,09/43] KVM: arm64: Allow passing machine type in KVM creation

Commit Message

Steven Price April 16, 2025, 1:41 p.m. UTC

Previously machine type was used purely for specifying the physical
address size of the guest. Reserve the higher bits to specify an ARM
specific machine type and declare a new type 'KVM_VM_TYPE_ARM_REALM'
used to create a realm guest.

Reviewed-by: Suzuki K Poulose <[e-mail]>
Signed-off-by: Steven Price <[e-mail]>
---
Changes since v7:
 * Add some documentation explaining the new machine type.
Changes since v6:
 * Make the check for kvm_rme_is_available more visible and report an
   error code of -EPERM (instead of -EINVAL) to make it explicit that
   the kernel supports RME, but the platform doesn't.
---
 Documentation/virt/kvm/api.rst | 16 ++++++++++++++--
 arch/arm64/kvm/arm.c           | 15 +++++++++++++++
 arch/arm64/kvm/mmu.c           |  3 ---
 include/uapi/linux/kvm.h       | 19 +++++++++++++++----
 4 files changed, 44 insertions(+), 9 deletions(-)

Patch

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 99ba6c82cf37..54ae0b98030e 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -181,8 +181,20 @@  flag KVM_VM_MIPS_VZ.
 ARM64:
 ^^^^^^
 
-On arm64, the physical address size for a VM (IPA Size limit) is limited
-to 40bits by default. The limit can be configured if the host supports the
+On arm64, the machine type identifier is used to encode a type and the
+physical address size for the VM. The lower byte (bits[7-0]) encode the
+address size and the upper bits[11-8] encode a machine type. The machine
+types that might be available are:
+
+ ======================   ============================================
+ KVM_VM_TYPE_ARM_NORMAL   A standard VM
+ KVM_VM_TYPE_ARM_REALM    A "Realm" VM using the Arm Confidential
+                          Compute extensions, the VM's memory is
+                          protected from the host.
+ ======================   ============================================
+
+The physical address size for a VM (IPA Size limit) is limited to 40bits
+by default. The limit can be configured if the host supports the
 extension KVM_CAP_ARM_VM_IPA_SIZE. When supported, use
 KVM_VM_TYPE_ARM_IPA_SIZE(IPA_Bits) to set the size in the machine type
 identifier, where IPA_Bits is the maximum width of any physical
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index c24448966529..ba55950e6a6e 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -172,6 +172,21 @@  int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	mutex_unlock(&kvm->lock);
 #endif
 
+	if (type & ~(KVM_VM_TYPE_ARM_MASK | KVM_VM_TYPE_ARM_IPA_SIZE_MASK))
+		return -EINVAL;
+
+	switch (type & KVM_VM_TYPE_ARM_MASK) {
+	case KVM_VM_TYPE_ARM_NORMAL:
+		break;
+	case KVM_VM_TYPE_ARM_REALM:
+		if (!static_branch_unlikely(&kvm_rme_is_available))
+			return -EPERM;
+		kvm->arch.is_realm = true;
+		break;
+	default:
+		return -EINVAL;
+	}
+
 	kvm_init_nested(kvm);
 
 	ret = kvm_share_hyp(kvm, kvm + 1);
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 5957a07de86d..7531211f7e25 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -886,9 +886,6 @@  static int kvm_init_ipa_range(struct kvm *kvm,
 	if (kvm_is_realm(kvm))
 		kvm_ipa_limit = kvm_realm_ipa_limit();
 
-	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/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 0b8479985581..957e4646ec99 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -644,14 +644,25 @@  struct kvm_enable_cap {
 #define KVM_S390_SIE_PAGE_OFFSET 1
 
 /*
- * On arm64, machine type can be used to request the physical
- * address size for the VM. Bits[7-0] are reserved for the guest
- * PA size shift (i.e, log2(PA_Size)). For backward compatibility,
- * value 0 implies the default IPA size, 40bits.
+ * On arm64, machine type can be used to request both the machine type and
+ * the physical address size for the VM.
+ *
+ * Bits[11-8] are reserved for the ARM specific machine type.
+ *
+ * Bits[7-0] are reserved for the guest PA size shift (i.e, log2(PA_Size)).
+ * For backward compatibility, value 0 implies the default IPA size, 40bits.
  */
+#define KVM_VM_TYPE_ARM_SHIFT		8
+#define KVM_VM_TYPE_ARM_MASK		(0xfULL << KVM_VM_TYPE_ARM_SHIFT)
+#define KVM_VM_TYPE_ARM(_type)		\
+	(((_type) << KVM_VM_TYPE_ARM_SHIFT) & KVM_VM_TYPE_ARM_MASK)
+#define KVM_VM_TYPE_ARM_NORMAL		KVM_VM_TYPE_ARM(0)
+#define KVM_VM_TYPE_ARM_REALM		KVM_VM_TYPE_ARM(1)
+
 #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)
+
 /*
  * ioctls for /dev/kvm fds:
  */