Merge tag 'kvm-x86-selftests-6.6' of https://github.com/kvm-x86/linux into HEAD

KVM: x86: Selftests changes for 6.6:

 - Add testcases to x86's sync_regs_test for detecting KVM TOCTOU bugs

 - Add support for printf() in guest code and covert all guest asserts to use
   printf-based reporting

 - Clean up the PMU event filter test and add new testcases

 - Include x86 selftests in the KVM x86 MAINTAINERS entry

56 files changed, 1389 insertions, 468 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 4cc6bf79fdd8..87e1e0e86f6c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11500,6 +11500,8 @@ F:	arch/x86/include/uapi/asm/svm.h
 F:	arch/x86/include/uapi/asm/vmx.h
 F:	arch/x86/kvm/
 F:	arch/x86/kvm/*/
+F:	tools/testing/selftests/kvm/*/x86_64/
+F:	tools/testing/selftests/kvm/x86_64/
 
 KERNFS
 M:	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 704596936d94..94fa36ee073c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11798,15 +11798,22 @@ static int sync_regs(struct kvm_vcpu *vcpu)
 		__set_regs(vcpu, &vcpu->run->s.regs.regs);
 		vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_REGS;
 	}
+
 	if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_SREGS) {
-		if (__set_sregs(vcpu, &vcpu->run->s.regs.sregs))
+		struct kvm_sregs sregs = vcpu->run->s.regs.sregs;
+
+		if (__set_sregs(vcpu, &sregs))
 			return -EINVAL;
+
 		vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_SREGS;
 	}
+
 	if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_EVENTS) {
-		if (kvm_vcpu_ioctl_x86_set_vcpu_events(
-				vcpu, &vcpu->run->s.regs.events))
+		struct kvm_vcpu_events events = vcpu->run->s.regs.events;
+
+		if (kvm_vcpu_ioctl_x86_set_vcpu_events(vcpu, &events))
 			return -EINVAL;
+
 		vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_EVENTS;
 	}
 
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index c692cc86e7da..77026907968f 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -23,6 +23,7 @@ LIBKVM += lib/guest_modes.c
 LIBKVM += lib/io.c
 LIBKVM += lib/kvm_util.c
 LIBKVM += lib/memstress.c
+LIBKVM += lib/guest_sprintf.c
 LIBKVM += lib/rbtree.c
 LIBKVM += lib/sparsebit.c
 LIBKVM += lib/test_util.c
@@ -122,6 +123,7 @@ TEST_GEN_PROGS_x86_64 += access_tracking_perf_test
 TEST_GEN_PROGS_x86_64 += demand_paging_test
 TEST_GEN_PROGS_x86_64 += dirty_log_test
 TEST_GEN_PROGS_x86_64 += dirty_log_perf_test
+TEST_GEN_PROGS_x86_64 += guest_print_test
 TEST_GEN_PROGS_x86_64 += hardware_disable_test
 TEST_GEN_PROGS_x86_64 += kvm_create_max_vcpus
 TEST_GEN_PROGS_x86_64 += kvm_page_table_test
@@ -152,6 +154,7 @@ TEST_GEN_PROGS_aarch64 += access_tracking_perf_test
 TEST_GEN_PROGS_aarch64 += demand_paging_test
 TEST_GEN_PROGS_aarch64 += dirty_log_test
 TEST_GEN_PROGS_aarch64 += dirty_log_perf_test
+TEST_GEN_PROGS_aarch64 += guest_print_test
 TEST_GEN_PROGS_aarch64 += kvm_create_max_vcpus
 TEST_GEN_PROGS_aarch64 += kvm_page_table_test
 TEST_GEN_PROGS_aarch64 += memslot_modification_stress_test
@@ -168,6 +171,7 @@ TEST_GEN_PROGS_s390x += s390x/tprot
 TEST_GEN_PROGS_s390x += s390x/cmma_test
 TEST_GEN_PROGS_s390x += demand_paging_test
 TEST_GEN_PROGS_s390x += dirty_log_test
+TEST_GEN_PROGS_s390x += guest_print_test
 TEST_GEN_PROGS_s390x += kvm_create_max_vcpus
 TEST_GEN_PROGS_s390x += kvm_page_table_test
 TEST_GEN_PROGS_s390x += rseq_test
@@ -176,6 +180,7 @@ TEST_GEN_PROGS_s390x += kvm_binary_stats_test
 
 TEST_GEN_PROGS_riscv += demand_paging_test
 TEST_GEN_PROGS_riscv += dirty_log_test
+TEST_GEN_PROGS_riscv += guest_print_test
 TEST_GEN_PROGS_riscv += kvm_create_max_vcpus
 TEST_GEN_PROGS_riscv += kvm_page_table_test
 TEST_GEN_PROGS_riscv += set_memory_region_test
@@ -204,6 +209,7 @@ endif
 CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
 	-Wno-gnu-variable-sized-type-not-at-end -MD\
 	-fno-builtin-memcmp -fno-builtin-memcpy -fno-builtin-memset \
+	-fno-builtin-strnlen \
 	-fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \
 	-I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \
 	-I$(<D) -Iinclude/$(ARCH_DIR) -I ../rseq -I.. $(EXTRA_CFLAGS) \
diff --git a/tools/testing/selftests/kvm/aarch64/aarch32_id_regs.c b/tools/testing/selftests/kvm/aarch64/aarch32_id_regs.c
index 4951ac53d1f8..b90580840b22 100644
--- a/tools/testing/selftests/kvm/aarch64/aarch32_id_regs.c
+++ b/tools/testing/selftests/kvm/aarch64/aarch32_id_regs.c
@@ -98,7 +98,7 @@ static void test_user_raz_wi(struct kvm_vcpu *vcpu)
 		uint64_t val;
 
 		vcpu_get_reg(vcpu, reg_id, &val);
-		ASSERT_EQ(val, 0);
+		TEST_ASSERT_EQ(val, 0);
 
 		/*
 		 * Expect the ioctl to succeed with no effect on the register
@@ -107,7 +107,7 @@ static void test_user_raz_wi(struct kvm_vcpu *vcpu)
 		vcpu_set_reg(vcpu, reg_id, BAD_ID_REG_VAL);
 
 		vcpu_get_reg(vcpu, reg_id, &val);
-		ASSERT_EQ(val, 0);
+		TEST_ASSERT_EQ(val, 0);
 	}
 }
 
@@ -127,14 +127,14 @@ static void test_user_raz_invariant(struct kvm_vcpu *vcpu)
 		uint64_t val;
 
 		vcpu_get_reg(vcpu, reg_id, &val);
-		ASSERT_EQ(val, 0);
+		TEST_ASSERT_EQ(val, 0);
 
 		r = __vcpu_set_reg(vcpu, reg_id, BAD_ID_REG_VAL);
 		TEST_ASSERT(r < 0 && errno == EINVAL,
 			    "unexpected KVM_SET_ONE_REG error: r=%d, errno=%d", r, errno);
 
 		vcpu_get_reg(vcpu, reg_id, &val);
-		ASSERT_EQ(val, 0);
+		TEST_ASSERT_EQ(val, 0);
 	}
 }
 
diff --git a/tools/testing/selftests/kvm/aarch64/arch_timer.c b/tools/testing/selftests/kvm/aarch64/arch_timer.c
index 8ef370924a02..274b8465b42a 100644
--- a/tools/testing/selftests/kvm/aarch64/arch_timer.c
+++ b/tools/testing/selftests/kvm/aarch64/arch_timer.c
@@ -19,7 +19,6 @@
  *
  * Copyright (c) 2021, Google LLC.
  */
-
 #define _GNU_SOURCE
 
 #include <stdlib.h>
@@ -155,11 +154,13 @@ static void guest_validate_irq(unsigned int intid,
 	xcnt_diff_us = cycles_to_usec(xcnt - shared_data->xcnt);
 
 	/* Make sure we are dealing with the correct timer IRQ */
-	GUEST_ASSERT_2(intid == timer_irq, intid, timer_irq);
+	GUEST_ASSERT_EQ(intid, timer_irq);
 
 	/* Basic 'timer condition met' check */
-	GUEST_ASSERT_3(xcnt >= cval, xcnt, cval, xcnt_diff_us);
-	GUEST_ASSERT_1(xctl & CTL_ISTATUS, xctl);
+	__GUEST_ASSERT(xcnt >= cval,
+		       "xcnt = 0x%llx, cval = 0x%llx, xcnt_diff_us = 0x%llx",
+		       xcnt, cval, xcnt_diff_us);
+	__GUEST_ASSERT(xctl & CTL_ISTATUS, "xcnt = 0x%llx", xcnt);
 
 	WRITE_ONCE(shared_data->nr_iter, shared_data->nr_iter + 1);
 }
@@ -192,8 +193,7 @@ static void guest_run_stage(struct test_vcpu_shared_data *shared_data,
 			TIMER_TEST_ERR_MARGIN_US);
 
 		irq_iter = READ_ONCE(shared_data->nr_iter);
-		GUEST_ASSERT_2(config_iter + 1 == irq_iter,
-				config_iter + 1, irq_iter);
+		GUEST_ASSERT_EQ(config_iter + 1, irq_iter);
 	}
 }
 
@@ -243,13 +243,9 @@ static void *test_vcpu_run(void *arg)
 		break;
 	case UCALL_ABORT:
 		sync_global_from_guest(vm, *shared_data);
-		REPORT_GUEST_ASSERT_N(uc, "values: %lu, %lu; %lu, vcpu %u; stage; %u; iter: %u",
-				      GUEST_ASSERT_ARG(uc, 0),
-				      GUEST_ASSERT_ARG(uc, 1),
-				      GUEST_ASSERT_ARG(uc, 2),
-				      vcpu_idx,
-				      shared_data->guest_stage,
-				      shared_data->nr_iter);
+		fprintf(stderr, "Guest assert failed,  vcpu %u; stage; %u; iter: %u\n",
+			vcpu_idx, shared_data->guest_stage, shared_data->nr_iter);
+		REPORT_GUEST_ASSERT(uc);
 		break;
 	default:
 		TEST_FAIL("Unexpected guest exit\n");
diff --git a/tools/testing/selftests/kvm/aarch64/debug-exceptions.c b/tools/testing/selftests/kvm/aarch64/debug-exceptions.c
index 637be796086f..f5b6cb3a0019 100644
--- a/tools/testing/selftests/kvm/aarch64/debug-exceptions.c
+++ b/tools/testing/selftests/kvm/aarch64/debug-exceptions.c
@@ -365,7 +365,7 @@ static void guest_wp_handler(struct ex_regs *regs)
 
 static void guest_ss_handler(struct ex_regs *regs)
 {
-	GUEST_ASSERT_1(ss_idx < 4, ss_idx);
+	__GUEST_ASSERT(ss_idx < 4, "Expected index < 4, got '%u'", ss_idx);
 	ss_addr[ss_idx++] = regs->pc;
 	regs->pstate |= SPSR_SS;
 }
@@ -410,8 +410,8 @@ static void guest_code_ss(int test_cnt)
 		/* Userspace disables Single Step when the end is nigh. */
 		asm volatile("iter_ss_end:\n");
 
-		GUEST_ASSERT(bvr == w_bvr);
-		GUEST_ASSERT(wvr == w_wvr);
+		GUEST_ASSERT_EQ(bvr, w_bvr);
+		GUEST_ASSERT_EQ(wvr, w_wvr);
 	}
 	GUEST_DONE();
 }
@@ -450,7 +450,7 @@ static void test_guest_debug_exceptions(uint8_t bpn, uint8_t wpn, uint8_t ctx_bp
 	vcpu_run(vcpu);
 	switch (get_ucall(vcpu, &uc)) {
 	case UCALL_ABORT:
-		REPORT_GUEST_ASSERT_2(uc, "values: %#lx, %#lx");
+		REPORT_GUEST_ASSERT(uc);
 		break;
 	case UCALL_DONE:
 		goto done;
diff --git a/tools/testing/selftests/kvm/aarch64/hypercalls.c b/tools/testing/selftests/kvm/aarch64/hypercalls.c
index bef1499fb465..31f66ba97228 100644
--- a/tools/testing/selftests/kvm/aarch64/hypercalls.c
+++ b/tools/testing/selftests/kvm/aarch64/hypercalls.c
@@ -8,7 +8,6 @@
  * hypercalls are properly masked or unmasked to the guest when disabled or
  * enabled from the KVM userspace, respectively.
  */
-
 #include <errno.h>
 #include <linux/arm-smccc.h>
 #include <asm/kvm.h>
@@ -105,15 +104,17 @@ static void guest_test_hvc(const struct test_hvc_info *hc_info)
 		switch (stage) {
 		case TEST_STAGE_HVC_IFACE_FEAT_DISABLED:
 		case TEST_STAGE_HVC_IFACE_FALSE_INFO:
-			GUEST_ASSERT_3(res.a0 == SMCCC_RET_NOT_SUPPORTED,
-					res.a0, hc_info->func_id, hc_info->arg1);
+			__GUEST_ASSERT(res.a0 == SMCCC_RET_NOT_SUPPORTED,
+				       "a0 = 0x%lx, func_id = 0x%x, arg1 = 0x%llx, stage = %u",
+					res.a0, hc_info->func_id, hc_info->arg1, stage);
 			break;
 		case TEST_STAGE_HVC_IFACE_FEAT_ENABLED:
-			GUEST_ASSERT_3(res.a0 != SMCCC_RET_NOT_SUPPORTED,
-					res.a0, hc_info->func_id, hc_info->arg1);
+			__GUEST_ASSERT(res.a0 != SMCCC_RET_NOT_SUPPORTED,
+				       "a0 = 0x%lx, func_id = 0x%x, arg1 = 0x%llx, stage = %u",
+					res.a0, hc_info->func_id, hc_info->arg1, stage);
 			break;
 		default:
-			GUEST_ASSERT_1(0, stage);
+			GUEST_FAIL("Unexpected stage = %u", stage);
 		}
 	}
 }
@@ -132,7 +133,7 @@ static void guest_code(void)
 			guest_test_hvc(false_hvc_info);
 			break;
 		default:
-			GUEST_ASSERT_1(0, stage);
+			GUEST_FAIL("Unexpected stage = %u", stage);
 		}
 
 		GUEST_SYNC(stage);
@@ -290,10 +291,7 @@ static void test_run(void)
 			guest_done = true;
 			break;
 		case UCALL_ABORT:
-			REPORT_GUEST_ASSERT_N(uc, "values: 0x%lx, 0x%lx; 0x%lx, stage: %u",
-					      GUEST_ASSERT_ARG(uc, 0),
-					      GUEST_ASSERT_ARG(uc, 1),
-					      GUEST_ASSERT_ARG(uc, 2), stage);
+			REPORT_GUEST_ASSERT(uc);
 			break;
 		default:
 			TEST_FAIL("Unexpected guest exit\n");
diff --git a/tools/testing/selftests/kvm/aarch64/page_fault_test.c b/tools/testing/selftests/kvm/aarch64/page_fault_test.c
index df10f1ffa20d..47bb914ab2fa 100644
--- a/tools/testing/selftests/kvm/aarch64/page_fault_test.c
+++ b/tools/testing/selftests/kvm/aarch64/page_fault_test.c
@@ -7,7 +7,6 @@
  * hugetlbfs with a hole). It checks that the expected handling method is
  * called (e.g., uffd faults with the right address and write/read flag).
  */
-
 #define _GNU_SOURCE
 #include <linux/bitmap.h>
 #include <fcntl.h>
@@ -293,12 +292,12 @@ static void guest_code(struct test_desc *test)
 
 static void no_dabt_handler(struct ex_regs *regs)
 {
-	GUEST_ASSERT_1(false, read_sysreg(far_el1));
+	GUEST_FAIL("Unexpected dabt, far_el1 = 0x%llx", read_sysreg(far_el1));
 }
 
 static void no_iabt_handler(struct ex_regs *regs)
 {
-	GUEST_ASSERT_1(false, regs->pc);
+	GUEST_FAIL("Unexpected iabt, pc = 0x%lx", regs->pc);
 }
 
 static struct uffd_args {
@@ -318,7 +317,7 @@ static int uffd_generic_handler(int uffd_mode, int uffd, struct uffd_msg *msg,
 
 	TEST_ASSERT(uffd_mode == UFFDIO_REGISTER_MODE_MISSING,
 		    "The only expected UFFD mode is MISSING");
-	ASSERT_EQ(addr, (uint64_t)args->hva);
+	TEST_ASSERT_EQ(addr, (uint64_t)args->hva);
 
 	pr_debug("uffd fault: addr=%p write=%d\n",
 		 (void *)addr, !!(flags & UFFD_PAGEFAULT_FLAG_WRITE));
@@ -432,7 +431,7 @@ static void mmio_on_test_gpa_handler(struct kvm_vm *vm, struct kvm_run *run)
 	region = vm_get_mem_region(vm, MEM_REGION_TEST_DATA);
 	hva = (void *)region->region.userspace_addr;
 
-	ASSERT_EQ(run->mmio.phys_addr, region->region.guest_phys_addr);
+	TEST_ASSERT_EQ(run->mmio.phys_addr, region->region.guest_phys_addr);
 
 	memcpy(hva, run->mmio.data, run->mmio.len);
 	events.mmio_exits += 1;
@@ -631,9 +630,9 @@ static void setup_default_handlers(struct test_desc *test)
 
 static void check_event_counts(struct test_desc *test)
 {
-	ASSERT_EQ(test->expected_events.uffd_faults, events.uffd_faults);
-	ASSERT_EQ(test->expected_events.mmio_exits, events.mmio_exits);
-	ASSERT_EQ(test->expected_events.fail_vcpu_runs, events.fail_vcpu_runs);
+	TEST_ASSERT_EQ(test->expected_events.uffd_faults, events.uffd_faults);
+	TEST_ASSERT_EQ(test->expected_events.mmio_exits, events.mmio_exits);
+	TEST_ASSERT_EQ(test->expected_events.fail_vcpu_runs, events.fail_vcpu_runs);
 }
 
 static void print_test_banner(enum vm_guest_mode mode, struct test_params *p)
@@ -679,7 +678,7 @@ static void vcpu_run_loop(struct kvm_vm *vm, struct kvm_vcpu *vcpu,
 			}
 			break;
 		case UCALL_ABORT:
-			REPORT_GUEST_ASSERT_2(uc, "values: %#lx, %#lx");
+			REPORT_GUEST_ASSERT(uc);
 			break;
 		case UCALL_DONE:
 			goto done;
diff --git a/tools/testing/selftests/kvm/aarch64/vgic_irq.c b/tools/testing/selftests/kvm/aarch64/vgic_irq.c
index 90d854e0fcff..2e64b4856e38 100644
--- a/tools/testing/selftests/kvm/aarch64/vgic_irq.c
+++ b/tools/testing/selftests/kvm/aarch64/vgic_irq.c
@@ -7,7 +7,6 @@
  * host to inject a specific intid via a GUEST_SYNC call, and then checks that
  * it received it.
  */
-
 #include <asm/kvm.h>
 #include <asm/kvm_para.h>
 #include <sys/eventfd.h>
@@ -781,7 +780,7 @@ static void test_vgic(uint32_t nr_irqs, bool level_sensitive, bool eoi_split)
 			run_guest_cmd(vcpu, gic_fd, &inject_args, &args);
 			break;
 		case UCALL_ABORT:
-			REPORT_GUEST_ASSERT_2(uc, "values: %#lx, %#lx");
+			REPORT_GUEST_ASSERT(uc);
 			break;
 		case UCALL_DONE:
 			goto done;
diff --git a/tools/testing/selftests/kvm/guest_print_test.c b/tools/testing/selftests/kvm/guest_print_test.c
new file mode 100644
index 000000000000..41230b746190
--- /dev/null
+++ b/tools/testing/selftests/kvm/guest_print_test.c
@@ -0,0 +1,219 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * A test for GUEST_PRINTF
+ *
+ * Copyright 2022, Google, Inc. and/or its affiliates.
+ */
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+
+struct guest_vals {
+	uint64_t a;
+	uint64_t b;
+	uint64_t type;
+};
+
+static struct guest_vals vals;
+
+/* GUEST_PRINTF()/GUEST_ASSERT_FMT() does not support float or double. */
+#define TYPE_LIST					\
+TYPE(test_type_i64,  I64,  "%ld",   int64_t)		\
+TYPE(test_type_u64,  U64u, "%lu",   uint64_t)		\
+TYPE(test_type_x64,  U64x, "0x%lx", uint64_t)		\
+TYPE(test_type_X64,  U64X, "0x%lX", uint64_t)		\
+TYPE(test_type_u32,  U32u, "%u",    uint32_t)		\
+TYPE(test_type_x32,  U32x, "0x%x",  uint32_t)		\
+TYPE(test_type_X32,  U32X, "0x%X",  uint32_t)		\
+TYPE(test_type_int,  INT,  "%d",    int)		\
+TYPE(test_type_char, CHAR, "%c",    char)		\
+TYPE(test_type_str,  STR,  "'%s'",  const char *)	\
+TYPE(test_type_ptr,  PTR,  "%p",    uintptr_t)
+
+enum args_type {
+#define TYPE(fn, ext, fmt_t, T) TYPE_##ext,
+	TYPE_LIST
+#undef TYPE
+};
+
+static void run_test(struct kvm_vcpu *vcpu, const char *expected_printf,
+		     const char *expected_assert);
+
+#define BUILD_TYPE_STRINGS_AND_HELPER(fn, ext, fmt_t, T)		     \
+const char *PRINTF_FMT_##ext = "Got params a = " fmt_t " and b = " fmt_t;    \
+const char *ASSERT_FMT_##ext = "Expected " fmt_t ", got " fmt_t " instead";  \
+static void fn(struct kvm_vcpu *vcpu, T a, T b)				     \
+{									     \
+	char expected_printf[UCALL_BUFFER_LEN];				     \
+	char expected_assert[UCALL_BUFFER_LEN];				     \
+									     \
+	snprintf(expected_printf, UCALL_BUFFER_LEN, PRINTF_FMT_##ext, a, b); \
+	snprintf(expected_assert, UCALL_BUFFER_LEN, ASSERT_FMT_##ext, a, b); \
+	vals = (struct guest_vals){ (uint64_t)a, (uint64_t)b, TYPE_##ext };  \
+	sync_global_to_guest(vcpu->vm, vals);				     \
+	run_test(vcpu, expected_printf, expected_assert);		     \
+}
+
+#define TYPE(fn, ext, fmt_t, T) \
+		BUILD_TYPE_STRINGS_AND_HELPER(fn, ext, fmt_t, T)
+	TYPE_LIST
+#undef TYPE
+
+static void guest_code(void)
+{
+	while (1) {
+		switch (vals.type) {
+#define TYPE(fn, ext, fmt_t, T)							\
+		case TYPE_##ext:						\
+			GUEST_PRINTF(PRINTF_FMT_##ext, vals.a, vals.b);		\
+			__GUEST_ASSERT(vals.a == vals.b,			\
+				       ASSERT_FMT_##ext, vals.a, vals.b);	\
+			break;
+		TYPE_LIST
+#undef TYPE
+		default:
+			GUEST_SYNC(vals.type);
+		}
+
+		GUEST_DONE();
+	}
+}
+
+/*
+ * Unfortunately this gets a little messy because 'assert_msg' doesn't
+ * just contains the matching string, it also contains additional assert
+ * info.  Fortunately the part that matches should be at the very end of
+ * 'assert_msg'.
+ */
+static void ucall_abort(const char *assert_msg, const char *expected_assert_msg)
+{
+	int len_str = strlen(assert_msg);
+	int len_substr = strlen(expected_assert_msg);
+	int offset = len_str - len_substr;
+
+	TEST_ASSERT(len_substr <= len_str,
+		    "Expected '%s' to be a substring of '%s'\n",
+		    assert_msg, expected_assert_msg);
+
+	TEST_ASSERT(strcmp(&assert_msg[offset], expected_assert_msg) == 0,
+		    "Unexpected mismatch. Expected: '%s', got: '%s'",
+		    expected_assert_msg, &assert_msg[offset]);
+}
+
+static void run_test(struct kvm_vcpu *vcpu, const char *expected_printf,
+		     const char *expected_assert)
+{
+	struct kvm_run *run = vcpu->run;
+	struct ucall uc;
+
+	while (1) {
+		vcpu_run(vcpu);
+
+		TEST_ASSERT(run->exit_reason == UCALL_EXIT_REASON,
+			    "Unexpected exit reason: %u (%s),\n",
+			    run->exit_reason, exit_reason_str(run->exit_reason));
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_SYNC:
+			TEST_FAIL("Unknown 'args_type' = %lu", uc.args[1]);
+			break;
+		case UCALL_PRINTF:
+			TEST_ASSERT(strcmp(uc.buffer, expected_printf) == 0,
+				    "Unexpected mismatch. Expected: '%s', got: '%s'",
+				    expected_printf, uc.buffer);
+			break;
+		case UCALL_ABORT:
+			ucall_abort(uc.buffer, expected_assert);
+			break;
+		case UCALL_DONE:
+			return;
+		default:
+			TEST_FAIL("Unknown ucall %lu", uc.cmd);
+		}
+	}
+}
+
+static void guest_code_limits(void)
+{
+	char test_str[UCALL_BUFFER_LEN + 10];
+
+	memset(test_str, 'a', sizeof(test_str));
+	test_str[sizeof(test_str) - 1] = 0;
+
+	GUEST_PRINTF("%s", test_str);
+}
+
+static void test_limits(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_run *run;
+	struct kvm_vm *vm;
+	struct ucall uc;
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code_limits);
+	run = vcpu->run;