[PATCH 3/3] KVM: selftests: Add test for race in kvm_recalculate_apic_map()

[Michal Luczaj <mhal@rbox.co>]

Keep switching between LAPIC_MODE_X2APIC and LAPIC_MODE_DISABLED during
APIC map construction.

Signed-off-by: Michal Luczaj <mhal@rbox.co>
---
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../kvm/x86_64/recalc_apic_map_race.c         | 110 ++++++++++++++++++
 2 files changed, 111 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/x86_64/recalc_apic_map_race.c

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 7a5ff646e7e7..c9b8f16fb23f 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -116,6 +116,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/sev_migrate_tests
 TEST_GEN_PROGS_x86_64 += x86_64/amx_test
 TEST_GEN_PROGS_x86_64 += x86_64/max_vcpuid_cap_test
 TEST_GEN_PROGS_x86_64 += x86_64/triple_fault_event_test
+TEST_GEN_PROGS_x86_64 += x86_64/recalc_apic_map_race
 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
diff --git a/tools/testing/selftests/kvm/x86_64/recalc_apic_map_race.c b/tools/testing/selftests/kvm/x86_64/recalc_apic_map_race.c
new file mode 100644
index 000000000000..1122df858623
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/recalc_apic_map_race.c
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * recalc_apic_map_race
+ *
+ * Test for a race condition in kvm_recalculate_apic_map().
+ */
+
+#include <sys/ioctl.h>
+#include <pthread.h>
+#include <time.h>
+
+#include "processor.h"
+#include "test_util.h"
+#include "kvm_util.h"
+#include "apic.h"
+
+#define TIMEOUT			5	/* seconds */
+#define STUFFING		100
+
+#define LAPIC_MODE_DISABLED	0
+#define LAPIC_MODE_X2APIC	(MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE)
+#define MAX_XAPIC_ID		0xff
+
+static int add_vcpu(struct kvm_vm *vm, long id)
+{
+	int vcpu = __vm_ioctl(vm, KVM_CREATE_VCPU, (void *)id);
+
+	static struct {
+		struct kvm_cpuid2 head;
+		struct kvm_cpuid_entry2 entry;
+	} cpuid = {
+		.head.nent = 1,
+		/* X86_FEATURE_X2APIC */
+		.entry = {
+			.function = 0x1,
+			.index = 0,
+			.ecx = 1UL << 21
+		}
+	};
+
+	ASSERT_EQ(ioctl(vcpu, KVM_SET_CPUID2, &cpuid.head), 0);
+
+	return vcpu;
+}
+
+static void set_apicbase(int vcpu, u64 mode)
+{
+	struct {
+		struct kvm_msrs head;
+		struct kvm_msr_entry entry;
+	} msr = {
+		.head.nmsrs = 1,
+		.entry = {
+			.index = MSR_IA32_APICBASE,
+			.data = mode
+		}
+	};
+
+	ASSERT_EQ(ioctl(vcpu, KVM_SET_MSRS, &msr.head), msr.head.nmsrs);
+}
+
+static void *race(void *arg)
+{
+	struct kvm_lapic_state state = {};
+	int vcpu = *(int *)arg;
+
+	while (1) {
+		/* Trigger kvm_recalculate_apic_map(). */
+		ioctl(vcpu, KVM_SET_LAPIC, &state);
+		pthread_testcancel();
+	}
+
+	return NULL;
+}
+
+int main(void)
+{
+	int vcpu0, vcpuN, i;
+	struct kvm_vm *vm;
+	pthread_t thread;
+	time_t t;
+
+	vm = vm_create_barebones();
+	vm_create_irqchip(vm);
+
+	vcpu0 = add_vcpu(vm, 0);
+	vcpuN = add_vcpu(vm, KVM_MAX_VCPUS);
+
+	static_assert(MAX_XAPIC_ID + STUFFING < KVM_MAX_VCPUS);
+	for (i = 0; i < STUFFING; ++i)
+		close(add_vcpu(vm, MAX_XAPIC_ID + i));
+
+	ASSERT_EQ(pthread_create(&thread, NULL, race, &vcpu0), 0);
+
+	pr_info("Testing recalc_apic_map_race...\n");
+
+	for (t = time(NULL) + TIMEOUT; time(NULL) < t;) {
+		set_apicbase(vcpuN, LAPIC_MODE_X2APIC);
+		set_apicbase(vcpuN, LAPIC_MODE_DISABLED);
+	}
+
+	ASSERT_EQ(pthread_cancel(thread), 0);
+	ASSERT_EQ(pthread_join(thread, NULL), 0);
+
+	close(vcpu0);
+	close(vcpuN);
+	kvm_vm_release(vm);
+
+	return 0;
+}
-- 
2.40.1