Disable all vcpu extensions which were enabled by default
if they were available in the risc-v host, and only enable
the desired one for a vcpu_config.

Suggested-by: Andrew Jones <redacted>
Signed-off-by: Haibo Xu <redacted>
---
 tools/testing/selftests/kvm/get-reg-list.c | 42 +++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/get-reg-list.c b/tools/testing/selftests/kvm/get-reg-list.c
index 3beb6b62de0a..612dabc61137 100644
--- a/tools/testing/selftests/kvm/get-reg-list.c
+++ b/tools/testing/selftests/kvm/get-reg-list.c

@@ -138,11 +138,50 @@ static struct kvm_vcpu *vcpu_config_get_vcpu(struct vcpu_reg_list *c, struct kvm
 	prepare_vcpu_init(c, &init);
 	vcpu = __vm_vcpu_add(vm, 0);
 	aarch64_vcpu_setup(vcpu, &init);
-	finalize_vcpu(vcpu, c);
 
 	return vcpu;
 }
 #else
+static inline bool vcpu_has_ext(struct kvm_vcpu *vcpu, int ext)
+{
+	int ret;
+	unsigned long value;
+
+	ret = __vcpu_get_reg(vcpu, RISCV_ISA_EXT_REG(ext), &value);
+	if (ret) {
+		printf("Failed to get ext %d", ext);
+		return false;
+	}
+
+	return !!value;
+}
+
+static void finalize_vcpu(struct kvm_vcpu *vcpu, struct vcpu_reg_list *c)
+{
+	struct vcpu_reg_sublist *s;
+
+	/*
+	 * Disable all extensions which were enabled by default
+	 * if they were available in the risc-v host.
+	 */
+	for (int i = 0; i < KVM_RISCV_ISA_EXT_MAX; i++) {
+		__vcpu_set_reg(vcpu, RISCV_ISA_EXT_REG(i), 0);
+	}

+
+	for_each_sublist(c, s) {
+		if (!s->feature)
+			continue;
+
+		/* Try to enable the desired extension */
+		__vcpu_set_reg(vcpu, RISCV_ISA_EXT_REG(s->feature), 1);
+
+		/* Double check whether the desired extension was enabled */
+		__TEST_REQUIRE(vcpu_has_ext(vcpu, s->feature),
+			       "%s: %s not available, skipping tests\n",
+			       config_name(c), s->name);
+	}
+}
+
 static struct kvm_vcpu *vcpu_config_get_vcpu(struct vcpu_reg_list *c, struct kvm_vm *vm)
 {
 	return __vm_vcpu_add(vm, 0);

@@ -178,6 +217,7 @@ static void run_test(struct vcpu_reg_list *c)
 
 	vm = vm_create_barebones();
 	vcpu = vcpu_config_get_vcpu(c, vm);
+	finalize_vcpu(vcpu, c);