[PATCH v2 4/7] KVM: arm64: MTE: Add KVM_CAP_ARM_MTE_PERM

[Aneesh Kumar K.V (Arm)]

This will be used by VMM to enable the usage of NoTagAccess memory
attribute while mapping pages not supporting allocating tags to guest
IPA.

Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@xxxxxxxxxx>
---
 Documentation/virt/kvm/api.rst    | 14 ++++++++++++++
 arch/arm64/include/asm/kvm_host.h |  7 +++++++
 arch/arm64/kvm/arm.c              | 11 +++++++++++
 include/uapi/linux/kvm.h          |  1 +
 4 files changed, 33 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 454c2aaa155e..e954fca76c27 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -9017,6 +9017,20 @@ Do not use KVM_X86_SW_PROTECTED_VM for "real" VMs, and especially not in
 production.  The behavior and effective ABI for software-protected VMs is
 unstable.
 
+8.42 KVM_CAP_ARM_MTE_PERM
+------------------------
+
+:Capability: KVM_CAP_ARM_MTE_PERM
+:Architectures: arm64
+:Type: vm
+
+This capability, if KVM_CHECK_EXTENSION indicates that it is available, means
+that the kernel has support for mapping memory regions not supporting
+allocations tags into a guest which enables KVM_CAP_ARM_MTE capability.
+
+In order to use this, it has to be activated by setting this capability via
+KVM_ENABLE_CAP ioctl on the VM fd.
+
 9. Known KVM API problems
 =========================
 
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index e18e9244d17a..ad2b488b99d5 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -331,6 +331,9 @@ struct kvm_arch {
 #define KVM_ARCH_FLAG_ID_REGS_INITIALIZED		7
 	/* Fine-Grained UNDEF initialised */
 #define KVM_ARCH_FLAG_FGU_INITIALIZED			8
+	/* Memory Tagging Extension NoTagAccess check enabled for the guest */
+#define KVM_ARCH_FLAG_MTE_PERM_ENABLED			9
+
 	unsigned long flags;
 
 	/* VM-wide vCPU feature set */
@@ -1417,6 +1420,10 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
 #define kvm_vm_has_ran_once(kvm)					\
 	(test_bit(KVM_ARCH_FLAG_HAS_RAN_ONCE, &(kvm)->arch.flags))
 
+#define kvm_has_mte_perm(kvm)					\
+	(system_supports_notagaccess() &&				\
+	 test_bit(KVM_ARCH_FLAG_MTE_PERM_ENABLED, &(kvm)->arch.flags))
+
 static inline bool __vcpu_has_feature(const struct kvm_arch *ka, int feature)
 {
 	return test_bit(feature, ka->vcpu_features);
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index a102c3aebdbc..fdcd2c1605d5 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -150,6 +150,14 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		}
 		mutex_unlock(&kvm->slots_lock);
 		break;
+	case KVM_CAP_ARM_MTE_PERM:
+		mutex_lock(&kvm->lock);
+		if (system_supports_notagaccess() && !kvm->created_vcpus) {
+			r = 0;
+			set_bit(KVM_ARCH_FLAG_MTE_PERM_ENABLED, &kvm->arch.flags);
+		}
+		mutex_unlock(&kvm->lock);
+		break;
 	default:
 		break;
 	}
@@ -418,6 +426,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES:
 		r = BIT(0);
 		break;
+	case KVM_CAP_ARM_MTE_PERM:
+		r = system_supports_notagaccess();
+		break;
 	default:
 		r = 0;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 502ea63b5d2e..4900ff577819 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -933,6 +933,7 @@ struct kvm_enable_cap {
 #define KVM_CAP_PRE_FAULT_MEMORY 236
 #define KVM_CAP_X86_APIC_BUS_CYCLES_NS 237
 #define KVM_CAP_X86_GUEST_MODE 238
+#define KVM_CAP_ARM_MTE_PERM 239
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
-- 
2.43.0