KVM: selftests: arm64: Test writes to CTR_EL0

Test that CTR_EL0 is modifiable from userspace, that changes are
visible to guests, and that they are preserved across a vCPU reset.
Signed-off-by: Sebastian Ott <sebott@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/r/20240619174036.483943-11-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

tools/testing/selftests/kvm/aarch64/set_id_regs.c

@@ -219,6 +219,7 @@ static void guest_code(void)
 	GUEST_REG_SYNC(SYS_ID_AA64MMFR1_EL1);
 	GUEST_REG_SYNC(SYS_ID_AA64MMFR2_EL1);
 	GUEST_REG_SYNC(SYS_ID_AA64ZFR0_EL1);
+	GUEST_REG_SYNC(SYS_CTR_EL0);
 
 	GUEST_DONE();
 }
@@ -490,11 +491,25 @@ static void test_clidr(struct kvm_vcpu *vcpu)
 	test_reg_vals[encoding_to_range_idx(SYS_CLIDR_EL1)] = clidr;
 }
 
+static void test_ctr(struct kvm_vcpu *vcpu)
+{
+	u64 ctr;
+
+	vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_CTR_EL0), &ctr);
+	ctr &= ~CTR_EL0_DIC_MASK;
+	if (ctr & CTR_EL0_IminLine_MASK)
+		ctr--;
+
+	vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_CTR_EL0), ctr);
+	test_reg_vals[encoding_to_range_idx(SYS_CTR_EL0)] = ctr;
+}
+
 static void test_vcpu_ftr_id_regs(struct kvm_vcpu *vcpu)
 {
 	u64 val;
 
 	test_clidr(vcpu);
+	test_ctr(vcpu);
 
 	vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MPIDR_EL1), &val);
 	val++;
@@ -525,6 +540,7 @@ static void test_reset_preserves_id_regs(struct kvm_vcpu *vcpu)
 		test_assert_id_reg_unchanged(vcpu, test_regs[i].reg);
 
 	test_assert_id_reg_unchanged(vcpu, SYS_CLIDR_EL1);
+	test_assert_id_reg_unchanged(vcpu, SYS_CTR_EL0);
 
 	ksft_test_result_pass("%s\n", __func__);
 }