diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 4a166588d99f..ed172a0b83b6 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -36,7 +36,7 @@ endif
 LIBKVM = lib/assert.c lib/elf.c lib/io.c lib/kvm_util.c lib/sparsebit.c lib/test_util.c
 LIBKVM_x86_64 = lib/x86_64/processor.c lib/x86_64/vmx.c lib/x86_64/svm.c lib/x86_64/ucall.c
 LIBKVM_aarch64 = lib/aarch64/processor.c lib/aarch64/ucall.c
-LIBKVM_s390x = lib/s390x/processor.c lib/s390x/ucall.c
+LIBKVM_s390x = lib/s390x/processor.c lib/s390x/ucall.c lib/s390x/diag318_test_handler.c
 
 TEST_GEN_PROGS_x86_64 = x86_64/cr4_cpuid_sync_test
 TEST_GEN_PROGS_x86_64 += x86_64/evmcs_test
diff --git a/tools/testing/selftests/kvm/include/s390x/diag318_test_handler.h b/tools/testing/selftests/kvm/include/s390x/diag318_test_handler.h
new file mode 100644
index 000000000000..d8233ebf317b
--- /dev/null
+++ b/tools/testing/selftests/kvm/include/s390x/diag318_test_handler.h
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Test handler for the s390x DIAGNOSE 0x0318 instruction.
+ *
+ * Copyright (C) 2020, IBM
+ */
+
+#ifndef SELFTEST_KVM_DIAG318_TEST_HANDLER
+#define SELFTEST_KVM_DIAG318_TEST_HANDLER
+
+uint64_t get_diag318_info(void);
+
+#endif
diff --git a/tools/testing/selftests/kvm/lib/s390x/diag318_test_handler.c b/tools/testing/selftests/kvm/lib/s390x/diag318_test_handler.c
new file mode 100644
index 000000000000..024e3a9ffda7
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/s390x/diag318_test_handler.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Test handler for the s390x DIAGNOSE 0x0318 instruction.
+ *
+ * Copyright (C) 2020, IBM
+ */
+
+#include "test_util.h"
+#include "kvm_util.h"
+
+#define VCPU_ID	5
+
+#define ICPT_INSTRUCTION	0x04
+#define IPA0_DIAG		0x8300
+
+static void guest_code(void)
+{
+	uint64_t diag318_info = 0x12345678;
+
+	asm volatile ("diag %0,0,0x318\n" : : "d" (diag318_info));
+}
+
+/*
+ * The DIAGNOSE 0x0318 instruction call must be handled via userspace. As such,
+ * we create an ad-hoc VM here to handle the instruction then extract the
+ * necessary data. It is up to the caller to decide what to do with that data.
+ */
+static uint64_t diag318_handler(void)
+{
+	struct kvm_vm *vm;
+	struct kvm_run *run;
+	uint64_t reg;
+	uint64_t diag318_info;
+
+	vm = vm_create_default(VCPU_ID, 0, guest_code);
+	vcpu_run(vm, VCPU_ID);
+	run = vcpu_state(vm, VCPU_ID);
+
+	TEST_ASSERT(run->exit_reason == KVM_EXIT_S390_SIEIC,
+		    "DIAGNOSE 0x0318 instruction was not intercepted");
+	TEST_ASSERT(run->s390_sieic.icptcode == ICPT_INSTRUCTION,
+		    "Unexpected intercept code: 0x%x", run->s390_sieic.icptcode);
+	TEST_ASSERT((run->s390_sieic.ipa & 0xff00) == IPA0_DIAG,
+		    "Unexpected IPA0 code: 0x%x", (run->s390_sieic.ipa & 0xff00));
+
+	reg = (run->s390_sieic.ipa & 0x00f0) >> 4;
+	diag318_info = run->s.regs.gprs[reg];
+
+	kvm_vm_free(vm);
+
+	return diag318_info;
+}
+
+uint64_t get_diag318_info(void)
+{
+	static uint64_t diag318_info;
+	static bool printed_skip;
+
+	/*
+	 * If KVM does not support diag318, then return 0 to
+	 * ensure tests do not break.
+	 */
+	if (!kvm_check_cap(KVM_CAP_S390_DIAG318)) {
+		if (!printed_skip) {
+			fprintf(stdout, "KVM_CAP_S390_DIAG318 not supported. "
+				"Skipping diag318 test.\n");
+			printed_skip = true;
+		}
+		return 0;
+	}
+
+	/*
+	 * If a test has previously requested the diag318 info,
+	 * then don't bother spinning up a temporary VM again.
+	 */
+	if (!diag318_info)
+		diag318_info = diag318_handler();
+
+	return diag318_info;
+}
diff --git a/tools/testing/selftests/kvm/s390x/resets.c b/tools/testing/selftests/kvm/s390x/resets.c
index b143db6d8693..d0416ba94ec5 100644
--- a/tools/testing/selftests/kvm/s390x/resets.c
+++ b/tools/testing/selftests/kvm/s390x/resets.c
@@ -12,6 +12,7 @@
 
 #include "test_util.h"
 #include "kvm_util.h"
+#include "diag318_test_handler.h"
 
 #define VCPU_ID 3
 #define LOCAL_IRQS 32
@@ -110,6 +111,8 @@ static void assert_clear(void)
 
 	TEST_ASSERT(!memcmp(sync_regs->vrs, regs_null, sizeof(sync_regs->vrs)),
 		    "vrs0-15 == 0 (sync_regs)");
+
+	TEST_ASSERT(sync_regs->diag318 == 0, "diag318 == 0 (sync_regs)");
 }
 
 static void assert_initial_noclear(void)
@@ -182,6 +185,7 @@ static void assert_normal(void)
 	test_one_reg(KVM_REG_S390_PFTOKEN, KVM_S390_PFAULT_TOKEN_INVALID);
 	TEST_ASSERT(sync_regs->pft == KVM_S390_PFAULT_TOKEN_INVALID,
 			"pft == 0xff.....  (sync_regs)");
+	TEST_ASSERT(sync_regs->diag318 == 0, "diag318 == 0 (sync_regs)");
 	assert_noirq();
 }
 
@@ -206,6 +210,7 @@ static void test_normal(void)
 	/* Create VM */
 	vm = vm_create_default(VCPU_ID, 0, guest_code_initial);
 	run = vcpu_state(vm, VCPU_ID);
+	run->s.regs.diag318 = get_diag318_info();
 	sync_regs = &run->s.regs;
 
 	vcpu_run(vm, VCPU_ID);
@@ -250,6 +255,7 @@ static void test_clear(void)
 	pr_info("Testing clear reset\n");
 	vm = vm_create_default(VCPU_ID, 0, guest_code_initial);
 	run = vcpu_state(vm, VCPU_ID);
+	run->s.regs.diag318 = get_diag318_info();
 	sync_regs = &run->s.regs;
 
 	vcpu_run(vm, VCPU_ID);
diff --git a/tools/testing/selftests/kvm/s390x/sync_regs_test.c b/tools/testing/selftests/kvm/s390x/sync_regs_test.c
index 5731ccf34917..caf7b8859a94 100644
--- a/tools/testing/selftests/kvm/s390x/sync_regs_test.c
+++ b/tools/testing/selftests/kvm/s390x/sync_regs_test.c
@@ -20,6 +20,7 @@
 
 #include "test_util.h"
 #include "kvm_util.h"
+#include "diag318_test_handler.h"
 
 #define VCPU_ID 5
 
@@ -70,7 +71,7 @@ static void compare_sregs(struct kvm_sregs *left, struct kvm_sync_regs *right)
 
 #undef REG_COMPARE
 
-#define TEST_SYNC_FIELDS   (KVM_SYNC_GPRS|KVM_SYNC_ACRS|KVM_SYNC_CRS)
+#define TEST_SYNC_FIELDS   (KVM_SYNC_GPRS|KVM_SYNC_ACRS|KVM_SYNC_CRS|KVM_SYNC_DIAG318)
 #define INVALID_SYNC_FIELD 0x80000000
 
 int main(int argc, char *argv[])
@@ -152,6 +153,12 @@ int main(int argc, char *argv[])
 
 	run->kvm_valid_regs = TEST_SYNC_FIELDS;
 	run->kvm_dirty_regs = KVM_SYNC_GPRS | KVM_SYNC_ACRS;
+
+	if (get_diag318_info() > 0) {
+		run->s.regs.diag318 = get_diag318_info();
+		run->kvm_dirty_regs |= KVM_SYNC_DIAG318;
+	}
+
 	rv = _vcpu_run(vm, VCPU_ID);
 	TEST_ASSERT(rv == 0, "vcpu_run failed: %d\n", rv);
 	TEST_ASSERT(run->exit_reason == KVM_EXIT_S390_SIEIC,
@@ -164,6 +171,9 @@ int main(int argc, char *argv[])
 	TEST_ASSERT(run->s.regs.acrs[0]  == 1 << 11,
 		    "acr0 sync regs value incorrect 0x%x.",
 		    run->s.regs.acrs[0]);
+	TEST_ASSERT(run->s.regs.diag318 == get_diag318_info(),
+		    "diag318 sync regs value incorrect 0x%llx.",
+		    run->s.regs.diag318);
 
 	vcpu_regs_get(vm, VCPU_ID, &regs);
 	compare_regs(&regs, &run->s.regs);
@@ -177,6 +187,7 @@ int main(int argc, char *argv[])
 	run->kvm_valid_regs = TEST_SYNC_FIELDS;
 	run->kvm_dirty_regs = 0;
 	run->s.regs.gprs[11] = 0xDEADBEEF;
+	run->s.regs.diag318 = 0x4B1D;
 	rv = _vcpu_run(vm, VCPU_ID);
 	TEST_ASSERT(rv == 0, "vcpu_run failed: %d\n", rv);
 	TEST_ASSERT(run->exit_reason == KVM_EXIT_S390_SIEIC,
@@ -186,6 +197,9 @@ int main(int argc, char *argv[])
 	TEST_ASSERT(run->s.regs.gprs[11] != 0xDEADBEEF,
 		    "r11 sync regs value incorrect 0x%llx.",
 		    run->s.regs.gprs[11]);
+	TEST_ASSERT(run->s.regs.diag318 != 0x4B1D,
+		    "diag318 sync regs value incorrect 0x%llx.",
+		    run->s.regs.diag318);
 
 	kvm_vm_free(vm);
 
