[PATCH 1/1] selftests: KVM: add test to print boottime wallclock

[Dongli Zhang]

As inspired by the discussion in [1], the boottime wallclock may drift due
to the fact that the masterclock (or host monotonic clock) and kvmclock are
calculated based on the algorithms in different domains.

This is to introduce a testcase to print the boottime wallclock
periodically to help diagnose the wallclock drift issue in the future.

The idea is to wrmsr the MSR_KVM_WALL_CLOCK_NEW, and read the boottime
wallclock nanoseconds immediately.

References:
[1] https://lore.kernel.org/all/20231001111313.77586-1-nsaenz@xxxxxxxxxx

Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/Makefile          |   3 +-
 .../selftests/kvm/x86_64/boottime_wallclock.c | 100 ++++++++++++++++++
 2 files changed, 102 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/kvm/x86_64/boottime_wallclock.c

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index a3bb36fb3cfc..fea05b0118de 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -60,7 +60,8 @@ LIBKVM_riscv += lib/riscv/ucall.c
 TEST_PROGS_x86_64 += x86_64/nx_huge_pages_test.sh
 
 # Compiled test targets
-TEST_GEN_PROGS_x86_64 = x86_64/cpuid_test
+TEST_GEN_PROGS_x86_64 = x86_64/boottime_wallclock
+TEST_GEN_PROGS_x86_64 += x86_64/cpuid_test
 TEST_GEN_PROGS_x86_64 += x86_64/cr4_cpuid_sync_test
 TEST_GEN_PROGS_x86_64 += x86_64/dirty_log_page_splitting_test
 TEST_GEN_PROGS_x86_64 += x86_64/get_msr_index_features
diff --git a/tools/testing/selftests/kvm/x86_64/boottime_wallclock.c b/tools/testing/selftests/kvm/x86_64/boottime_wallclock.c
new file mode 100644
index 000000000000..cc48c9b19920
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/boottime_wallclock.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 Oracle and/or its affiliates.
+ */
+
+#include <asm/kvm_para.h>
+#include <asm/pvclock-abi.h>
+
+#include "kvm_util.h"
+#include "processor.h"
+
+static int period = 10;
+
+#define GUEST_SYNC_WALLCLOCK(__stage, __val)                        \
+		GUEST_SYNC_ARGS(__stage, __val, 0, 0, 0)
+
+static void guest_main(vm_paddr_t wc_pa, struct pvclock_wall_clock *wc)
+{
+	uint64_t wallclock;
+
+	while (true) {
+		wrmsr(MSR_KVM_WALL_CLOCK_NEW, wc_pa);
+
+		wallclock = wc->sec * NSEC_PER_SEC + wc->nsec;
+
+		GUEST_SYNC_WALLCLOCK(0, wallclock);
+	}
+}
+
+static void handle_sync(struct ucall *uc)
+{
+	uint64_t wallclock;
+
+	wallclock = uc->args[2];
+
+	pr_info("Boottime wallclock value: %"PRIu64" ns\n", wallclock);
+}
+
+static void handle_abort(struct ucall *uc)
+{
+	REPORT_GUEST_ASSERT(*uc);
+}
+
+static void enter_guest(struct kvm_vcpu *vcpu)
+{
+	struct ucall uc;
+
+	while (true) {
+		vcpu_run(vcpu);
+
+		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_SYNC:
+			handle_sync(&uc);
+			break;
+		case UCALL_ABORT:
+			handle_abort(&uc);
+			return;
+		default:
+			TEST_ASSERT(0, "unhandled ucall: %ld\n", uc.cmd);
+			return;
+		}
+
+		sleep(period);
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	vm_vaddr_t wc_gva;
+	vm_paddr_t wc_gpa;
+	int opt;
+
+	while ((opt = getopt(argc, argv, "p:h")) != -1) {
+		switch (opt) {
+		case 'p':
+			period = atoi_positive("The period (seconds)", optarg);
+			break;
+		case 'h':
+		default:
+			pr_info("usage: %s [-p period (seconds)]\n", argv[0]);
+			exit(1);
+		}
+	}
+
+	pr_info("Capture boottime wallclock every %d seconds.\n", period);
+	pr_info("Stop with Ctrl + c.\n\n");
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_main);
+
+	wc_gva = vm_vaddr_alloc(vm, getpagesize(), 0x10000);
+	wc_gpa = addr_gva2gpa(vm, wc_gva);
+	vcpu_args_set(vcpu, 2, wc_gpa, wc_gva);
+
+	enter_guest(vcpu);
+	kvm_vm_free(vm);
+}
-- 
2.34.1