[PATCH 1/1] KVM: selftests: add kvmclock drift test

[Dongli Zhang]

There is kvmclock drift issue during the vCPU hotplug. It has been fixed by
the commit c52ffadc65e2 ("KVM: x86: Don't unnecessarily force masterclock
update on vCPU hotplug").

This is to add the test to verify if the master clock is updated when we
write 0 to MSR_IA32_TSC from the host side.

Here is the usage example on the KVM with the bugfix reverted.

$ ./kvm_clock_drift -v -p 5
kvmclock based on old pvclock_vcpu_time_info: 5012221999
  version:           2
  tsc_timestamp:     3277968
  system_time:       11849519
  tsc_to_system_mul: 2152530255
  tsc_shift:         0
  flags:             1

kvmclock based on new pvclock_vcpu_time_info: 5012222411
  version:           4
  tsc_timestamp:     9980576184
  system_time:       5012222411
  tsc_to_system_mul: 2152530255
  tsc_shift:         0
  flags:             1

==== Test Assertion Failure ====
  x86_64/kvm_clock_drift.c:216: clock_old == clock_new
  pid=14257 tid=14257 errno=4 - Interrupted system call
     1	0x000000000040277b: main at kvm_clock_drift.c:216
     2	0x00007f7766fa7e44: ?? ??:0
     3	0x000000000040286d: _start at ??:?
  kvmclock drift detected, old=5012221999, new=5012222411

Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../selftests/kvm/x86_64/kvm_clock_drift.c    | 223 ++++++++++++++++++
 2 files changed, 224 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/x86_64/kvm_clock_drift.c

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 4412b42d95de..c665d0d8d348 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -84,6 +84,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/hyperv_features
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_ipi
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_svm_test
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_tlb_flush
+TEST_GEN_PROGS_x86_64 += x86_64/kvm_clock_drift
 TEST_GEN_PROGS_x86_64 += x86_64/kvm_clock_test
 TEST_GEN_PROGS_x86_64 += x86_64/kvm_pv_test
 TEST_GEN_PROGS_x86_64 += x86_64/monitor_mwait_test
diff --git a/tools/testing/selftests/kvm/x86_64/kvm_clock_drift.c b/tools/testing/selftests/kvm/x86_64/kvm_clock_drift.c
new file mode 100644
index 000000000000..324f0dbc5762
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/kvm_clock_drift.c
@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * The kvmclock drift test. Emulate vCPU hotplug and online to verify if
+ * there is kvmclock drift.
+ *
+ * Adapted from steal_time.c
+ *
+ * Copyright (C) 2020, Red Hat, Inc.
+ * Copyright (C) 2024 Oracle and/or its affiliates.
+ */
+
+#include <asm/kvm_para.h>
+#include <asm/pvclock.h>
+#include <asm/pvclock-abi.h>
+#include <sys/stat.h>
+
+#include "kvm_util.h"
+#include "processor.h"
+
+#define NR_VCPUS		2
+#define NR_SLOTS		2
+#define KVMCLOCK_SIZE		sizeof(struct pvclock_vcpu_time_info)
+/*
+ * KVMCLOCK_GPA is identity mapped
+ */
+#define KVMCLOCK_GPA		(1 << 30)
+
+static uint64_t kvmclock_gpa = KVMCLOCK_GPA;
+
+static void guest_code(int cpu)
+{
+	struct pvclock_vcpu_time_info *kvmclock;
+
+	/*
+	 * vCPU#0 is to detect the change of pvclock_vcpu_time_info
+	 */
+	if (cpu == 0) {
+		GUEST_SYNC(0);
+
+		kvmclock = (struct pvclock_vcpu_time_info *) kvmclock_gpa;
+		wrmsr(MSR_KVM_SYSTEM_TIME_NEW, kvmclock_gpa | KVM_MSR_ENABLED);
+
+		/*
+		 * Backup the pvclock_vcpu_time_info before vCPU#1 hotplug
+		 */
+		kvmclock[1] = kvmclock[0];
+
+		GUEST_SYNC(2);
+		/*
+		 * Enter the guest to update pvclock_vcpu_time_info
+		 */
+		GUEST_SYNC(4);
+	}
+
+	/*
+	 * vCPU#1 is to emulate the vCPU hotplug
+	 */
+	if (cpu == 1) {
+		GUEST_SYNC(1);
+		/*
+		 * This is after the host side MSR_IA32_TSC
+		 */
+		GUEST_SYNC(3);
+	}
+}
+
+static void run_vcpu(struct kvm_vcpu *vcpu)
+{
+	struct ucall uc;
+
+	vcpu_run(vcpu);
+
+	switch (get_ucall(vcpu, &uc)) {
+	case UCALL_SYNC:
+	case UCALL_DONE:
+		break;
+	case UCALL_ABORT:
+		REPORT_GUEST_ASSERT(uc);
+	default:
+		TEST_ASSERT(false, "Unexpected exit: %s",
+			    exit_reason_str(vcpu->run->exit_reason));
+	}
+}
+
+static void kvmclock_dump(struct pvclock_vcpu_time_info *kvmclock)
+{
+	pr_info("  version:           %u\n", kvmclock->version);
+	pr_info("  tsc_timestamp:     %lu\n", kvmclock->tsc_timestamp);
+	pr_info("  system_time:       %lu\n", kvmclock->system_time);
+	pr_info("  tsc_to_system_mul: %u\n", kvmclock->tsc_to_system_mul);
+	pr_info("  tsc_shift:         %d\n", kvmclock->tsc_shift);
+	pr_info("  flags:             %u\n", kvmclock->flags);
+	pr_info("\n");
+}
+
+#define CLOCKSOURCE_PATH "/sys/devices/system/clocksource/clocksource0/current_clocksource"
+
+static void check_clocksource(void)
+{
+	char *clk_name;
+	struct stat st;
+	FILE *fp;
+
+	fp = fopen(CLOCKSOURCE_PATH, "r");
+	if (!fp) {
+		pr_info("failed to open clocksource file: %d; assuming TSC.\n",
+			errno);
+		return;
+	}
+
+	if (fstat(fileno(fp), &st)) {
+		pr_info("failed to stat clocksource file: %d; assuming TSC.\n",
+			errno);
+		goto out;
+	}
+
+	clk_name = malloc(st.st_size);
+	TEST_ASSERT(clk_name, "failed to allocate buffer to read file\n");
+
+	if (!fgets(clk_name, st.st_size, fp)) {
+		pr_info("failed to read clocksource file: %d; assuming TSC.\n",
+			ferror(fp));
+		goto out;
+	}
+
+	TEST_ASSERT(!strncmp(clk_name, "tsc\n", st.st_size),
+		    "clocksource not supported: %s", clk_name);
+out:
+	fclose(fp);
+}
+
+int main(int argc, char *argv[])
+{
+	struct pvclock_vcpu_time_info *kvmclock;
+	struct kvm_vcpu *vcpus[NR_VCPUS];
+	uint64_t clock_old, clock_new;
+	bool verbose = false;
+	unsigned int gpages;
+	struct kvm_vm *vm;
+	int period = 2;
+	uint64_t tsc;
+	int opt;
+
+	check_clocksource();
+
+	while ((opt = getopt(argc, argv, "p:vh")) != -1) {
+		switch (opt) {
+		case 'p':
+			period = atoi_positive("The period (seconds) between vCPU hotplug",
+					       optarg);
+			break;
+		case 'v':
+			verbose = true;
+			break;
+		case 'h':
+		default:
+			pr_info("usage: %s [-p period (seconds)] [-v]\n", argv[0]);
+			exit(1);
+		}
+	}
+
+	vm = vm_create_with_vcpus(NR_VCPUS, guest_code, vcpus);
+	gpages = vm_calc_num_guest_pages(VM_MODE_DEFAULT,
+					 KVMCLOCK_SIZE * NR_SLOTS);
+	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
+				    KVMCLOCK_GPA, 1, gpages, 0);
+	virt_map(vm, KVMCLOCK_GPA, KVMCLOCK_GPA, gpages);
+
+	vcpu_args_set(vcpus[0], 1, 0);
+	vcpu_args_set(vcpus[1], 1, 1);
+
+	/*
+	 * Run vCPU#0 and vCPU#1 to update both pvclock_vcpu_time_info and
+	 * master clock
+	 */
+	run_vcpu(vcpus[0]);
+	run_vcpu(vcpus[1]);
+
+	/*
+	 * Run vCPU#0 to backup the current pvclock_vcpu_time_info
+	 */
+	run_vcpu(vcpus[0]);
+
+	sleep(period);
+
+	/*
+	 * Emulate the hotplug of vCPU#1
+	 */
+	vcpu_set_msr(vcpus[1], MSR_IA32_TSC, 0);
+
+	/*
+	 * Emulate the online of vCPU#1
+	 */
+	run_vcpu(vcpus[1]);
+
+	/*
+	 * Run vCPU#0 to backup the new pvclock_vcpu_time_info to detect
+	 * if there is any change or kvmclock drift
+	 */
+	run_vcpu(vcpus[0]);
+
+	kvmclock = addr_gva2hva(vm, kvmclock_gpa);
+	tsc = kvmclock[0].tsc_timestamp;
+	clock_old = __pvclock_read_cycles(&kvmclock[1], tsc);
+	clock_new = __pvclock_read_cycles(&kvmclock[0], tsc);
+
+	if (verbose) {
+		pr_info("kvmclock based on old pvclock_vcpu_time_info: %lu\n",
+			clock_old);
+		kvmclock_dump(&kvmclock[1]);
+		pr_info("kvmclock based on new pvclock_vcpu_time_info: %lu\n",
+			clock_new);
+		kvmclock_dump(&kvmclock[0]);
+	}
+
+	TEST_ASSERT(clock_old == clock_new,
+		    "kvmclock drift detected, old=%lu, new=%lu",
+		    clock_old, clock_new);
+
+	kvm_vm_free(vm);
+
+	return 0;
+}

base-commit: f2a3fb7234e52f72ff4a38364dbf639cf4c7d6c6
-- 
2.34.1