[PATCH v2 09/16] KVM: arm64: Advertise a capability for MMIO guard

[Marc Zyngier]

In order for userspace to find out whether the MMIO guard is
exposed to a guest, expose a capability that says so.

We take this opportunity to make it incompatible with the NISV
option, as that would be rather counter-productive!

Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
 arch/arm64/kvm/arm.c        | 29 ++++++++++++++++++-----------
 arch/arm64/kvm/hypercalls.c | 14 ++++++++++++--
 include/uapi/linux/kvm.h    |  1 +
 3 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index ed9c89ec0b4f..1c9a7abe2728 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -81,32 +81,33 @@ int kvm_arch_check_processor_compat(void *opaque)
 int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 			    struct kvm_enable_cap *cap)
 {
-	int r;
+	int r = -EINVAL;
 
 	if (cap->flags)
 		return -EINVAL;
 
+	mutex_lock(&kvm->lock);
+
 	switch (cap->cap) {
 	case KVM_CAP_ARM_NISV_TO_USER:
-		r = 0;
-		set_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
-			&kvm->arch.flags);
+		/* This is incompatible with MMIO guard */
+		if (!test_bit(KVM_ARCH_FLAG_MMIO_GUARD, &kvm->arch.flags)) {
+			r = 0;
+			set_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
+				&kvm->arch.flags);
+		}
 		break;
 	case KVM_CAP_ARM_MTE:
-		mutex_lock(&kvm->lock);
-		if (!system_supports_mte() || kvm->created_vcpus) {
-			r = -EINVAL;
-		} else {
+		if (system_supports_mte() && !kvm->created_vcpus) {
 			r = 0;
 			set_bit(KVM_ARCH_FLAG_MTE_ENABLED, &kvm->arch.flags);
 		}
-		mutex_unlock(&kvm->lock);
 		break;
 	default:
-		r = -EINVAL;
 		break;
 	}
 
+	mutex_unlock(&kvm->lock);
 	return r;
 }
 
@@ -211,13 +212,19 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_IMMEDIATE_EXIT:
 	case KVM_CAP_VCPU_EVENTS:
 	case KVM_CAP_ARM_IRQ_LINE_LAYOUT_2:
-	case KVM_CAP_ARM_NISV_TO_USER:
 	case KVM_CAP_ARM_INJECT_EXT_DABT:
 	case KVM_CAP_SET_GUEST_DEBUG:
 	case KVM_CAP_VCPU_ATTRIBUTES:
 	case KVM_CAP_PTP_KVM:
 		r = 1;
 		break;
+	case KVM_CAP_ARM_NISV_TO_USER:
+		r = !test_bit(KVM_ARCH_FLAG_MMIO_GUARD, &kvm->arch.flags);
+		break;
+	case KVM_CAP_ARM_MMIO_GUARD:
+		r = !test_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
+			      &kvm->arch.flags);
+		break;
 	case KVM_CAP_SET_GUEST_DEBUG2:
 		return KVM_GUESTDBG_VALID_MASK;
 	case KVM_CAP_ARM_SET_DEVICE_ADDR:
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index c39aab55ecae..e4fade6a96f6 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -59,6 +59,14 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
 	val[3] = lower_32_bits(cycles);
 }
 
+static bool mmio_guard_allowed(struct kvm_vcpu *vcpu)
+{
+	return (!test_bit(KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER,
+			  &vcpu->kvm->arch.flags) &&
+		!vcpu_mode_is_32bit(vcpu));
+
+}
+
 int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 {
 	u32 func_id = smccc_get_function(vcpu);
@@ -131,7 +139,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 		val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
 		val[0] |= BIT(ARM_SMCCC_KVM_FUNC_PTP);
 		/* Only advertise MMIO guard to 64bit guests */
-		if (!vcpu_mode_is_32bit(vcpu)) {
+		if (mmio_guard_allowed(vcpu)) {
 			val[0] |= BIT(ARM_SMCCC_KVM_FUNC_MMIO_GUARD_INFO);
 			val[0] |= BIT(ARM_SMCCC_KVM_FUNC_MMIO_GUARD_ENROLL);
 			val[0] |= BIT(ARM_SMCCC_KVM_FUNC_MMIO_GUARD_MAP);
@@ -146,10 +154,12 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 			val[0] = PAGE_SIZE;
 		break;
 	case ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_ENROLL_FUNC_ID:
-		if (!vcpu_mode_is_32bit(vcpu)) {
+		mutex_lock(&vcpu->kvm->lock);
+		if (mmio_guard_allowed(vcpu)) {
 			set_bit(KVM_ARCH_FLAG_MMIO_GUARD, &vcpu->kvm->arch.flags);
 			val[0] = SMCCC_RET_SUCCESS;
 		}
+		mutex_unlock(&vcpu->kvm->lock);
 		break;
 	case ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_MAP_FUNC_ID:
 		if (!vcpu_mode_is_32bit(vcpu) &&
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index a067410ebea5..ef171186e7be 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1112,6 +1112,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_BINARY_STATS_FD 203
 #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
 #define KVM_CAP_ARM_MTE 205
+#define KVM_CAP_ARM_MMIO_GUARD 206
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
-- 
2.30.2