KVM: arm64: selftests: Provide kvm_arch_vm_post_create() in library code

In order to compel the default usage of EL2 in selftests, move
kvm_arch_vm_post_create() to library code and expose an opt-in for using
MTE by default.

Signed-off-by: Oliver Upton <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>

tools/testing/selftests/kvm/arm64/set_id_regs.c

···
 #include "test_util.h"
 #include <linux/bitfield.h>
 
-bool have_cap_arm_mte;
-
 enum ftr_type {
 	FTR_EXACT,			/* Use a predefined safe value */
 	FTR_LOWER_SAFE,			/* Smaller value is safe */
···
 	uint64_t mte_frac;
 	int idx, err;
 
-	if (!have_cap_arm_mte) {
+	val = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_ID_AA64PFR1_EL1));
+	mte = FIELD_GET(ID_AA64PFR1_EL1_MTE, val);
+	if (!mte) {
 		ksft_test_result_skip("MTE capability not supported, nothing to test\n");
 		return;
 	}
···
 	 * from unsupported (0xF) to supported (0).
 	 *
 	 */
-	val = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_ID_AA64PFR1_EL1));
-
-	mte = FIELD_GET(ID_AA64PFR1_EL1_MTE, val);
 	mte_frac = FIELD_GET(ID_AA64PFR1_EL1_MTE_frac, val);
 	if (mte != ID_AA64PFR1_EL1_MTE_MTE2 ||
 	    mte_frac != ID_AA64PFR1_EL1_MTE_frac_NI) {
···
 	ksft_test_result_pass("%s\n", __func__);
 }
 
-void kvm_arch_vm_post_create(struct kvm_vm *vm)
-{
-	if (vm_check_cap(vm, KVM_CAP_ARM_MTE)) {
-		vm_enable_cap(vm, KVM_CAP_ARM_MTE, 0);
-		have_cap_arm_mte = true;
-	}
-}
-
 int main(void)
 {
 	struct kvm_vcpu *vcpu;
···
 
 	TEST_REQUIRE(kvm_has_cap(KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES));
 	TEST_REQUIRE(kvm_has_cap(KVM_CAP_ARM_WRITABLE_IMP_ID_REGS));
+
+	test_wants_mte();
 
 	vm = vm_create(1);
 	vm_enable_cap(vm, KVM_CAP_ARM_WRITABLE_IMP_ID_REGS, 0);

tools/testing/selftests/kvm/include/arm64/processor.h

···
 /* Execute a Wait For Interrupt instruction. */
 void wfi(void);
 
+void test_wants_mte(void);
+
 #endif /* SELFTEST_KVM_PROCESSOR_H */

tools/testing/selftests/kvm/lib/arm64/processor.c

···
 {
 	asm volatile("wfi");
 }
+
+static bool request_mte;
+
+void test_wants_mte(void)
+{
+	request_mte = true;
+}
+
+void kvm_arch_vm_post_create(struct kvm_vm *vm)
+{
+	if (request_mte && vm_check_cap(vm, KVM_CAP_ARM_MTE))
+		vm_enable_cap(vm, KVM_CAP_ARM_MTE, 0);
+}