KVM: selftests: Test behavior of KVM_X86_DISABLE_EXITS_APERFMPERF

For a VCPU thread pinned to a single LPU, verify that interleaved host
and guest reads of IA32_[AM]PERF return strictly increasing values when
APERFMPERF exiting is disabled.

Run the test in both L1 and L2 to verify that KVM passes through the
APERF and MPERF MSRs when L1 doesn't want to intercept them (or any MSRs).

Signed-off-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20250530185239.2335185-4-jmattson@google.com
Co-developed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20250626001225.744268-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: jsmattsonjr

tools/testing/selftests/kvm/Makefile.kvm

@@ -134,6 +134,7 @@ TEST_GEN_PROGS_x86 += x86/amx_test
 TEST_GEN_PROGS_x86 += x86/max_vcpuid_cap_test
 TEST_GEN_PROGS_x86 += x86/triple_fault_event_test
 TEST_GEN_PROGS_x86 += x86/recalc_apic_map_test
+TEST_GEN_PROGS_x86 += x86/aperfmperf_test
 TEST_GEN_PROGS_x86 += access_tracking_perf_test
 TEST_GEN_PROGS_x86 += coalesced_io_test
 TEST_GEN_PROGS_x86 += dirty_log_perf_test

tools/testing/selftests/kvm/x86/aperfmperf_test.c

@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Test for KVM_X86_DISABLE_EXITS_APERFMPERF
+ *
+ * Copyright (C) 2025, Google LLC.
+ *
+ * Test the ability to disable VM-exits for rdmsr of IA32_APERF and
+ * IA32_MPERF. When these VM-exits are disabled, reads of these MSRs
+ * return the host's values.
+ *
+ * Note: Requires read access to /dev/cpu/<lpu>/msr to read host MSRs.
+ */
+
+#include <fcntl.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <asm/msr-index.h>
+
+#include "kvm_util.h"
+#include "processor.h"
+#include "svm_util.h"
+#include "test_util.h"
+#include "vmx.h"
+
+#define NUM_ITERATIONS 10000
+
+static int open_dev_msr(int cpu)
+{
+	char path[PATH_MAX];
+
+	snprintf(path, sizeof(path), "/dev/cpu/%d/msr", cpu);
+	return open_path_or_exit(path, O_RDONLY);
+}
+
+static uint64_t read_dev_msr(int msr_fd, uint32_t msr)
+{
+	uint64_t data;
+	ssize_t rc;
+
+	rc = pread(msr_fd, &data, sizeof(data), msr);
+	TEST_ASSERT(rc == sizeof(data), "Read of MSR 0x%x failed", msr);
+
+	return data;
+}
+
+static void guest_read_aperf_mperf(void)
+{
+	int i;
+
+	for (i = 0; i < NUM_ITERATIONS; i++)
+		GUEST_SYNC2(rdmsr(MSR_IA32_APERF), rdmsr(MSR_IA32_MPERF));
+}
+
+#define L2_GUEST_STACK_SIZE	64
+
+static void l2_guest_code(void)
+{
+	guest_read_aperf_mperf();
+	GUEST_DONE();
+}
+
+static void l1_svm_code(struct svm_test_data *svm)
+{
+	unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
+	struct vmcb *vmcb = svm->vmcb;
+
+	generic_svm_setup(svm, l2_guest_code, &l2_guest_stack[L2_GUEST_STACK_SIZE]);
+	run_guest(vmcb, svm->vmcb_gpa);
+}
+
+static void l1_vmx_code(struct vmx_pages *vmx)
+{
+	unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
+
+	GUEST_ASSERT_EQ(prepare_for_vmx_operation(vmx), true);
+	GUEST_ASSERT_EQ(load_vmcs(vmx), true);
+
+	prepare_vmcs(vmx, NULL, &l2_guest_stack[L2_GUEST_STACK_SIZE]);
+
+	/*
+	 * Enable MSR bitmaps (the bitmap itself is allocated, zeroed, and set
+	 * in the VMCS by prepare_vmcs()), as MSR exiting mandatory on Intel.
+	 */
+	vmwrite(CPU_BASED_VM_EXEC_CONTROL,
+		vmreadz(CPU_BASED_VM_EXEC_CONTROL) | CPU_BASED_USE_MSR_BITMAPS);
+
+	GUEST_ASSERT(!vmwrite(GUEST_RIP, (u64)l2_guest_code));
+	GUEST_ASSERT(!vmlaunch());
+}
+
+static void guest_code(void *nested_test_data)
+{
+	guest_read_aperf_mperf();
+
+	if (this_cpu_has(X86_FEATURE_SVM))
+		l1_svm_code(nested_test_data);
+	else if (this_cpu_has(X86_FEATURE_VMX))
+		l1_vmx_code(nested_test_data);
+	else
+		GUEST_DONE();
+
+	TEST_FAIL("L2 should have signaled 'done'");
+}
+
+static void guest_no_aperfmperf(void)
+{
+	uint64_t msr_val;
+	uint8_t vector;
+
+	vector = rdmsr_safe(MSR_IA32_APERF, &msr_val);
+	GUEST_ASSERT(vector == GP_VECTOR);
+
+	vector = rdmsr_safe(MSR_IA32_APERF, &msr_val);
+	GUEST_ASSERT(vector == GP_VECTOR);
+
+	GUEST_DONE();
+}
+
+int main(int argc, char *argv[])
+{
+	const bool has_nested = kvm_cpu_has(X86_FEATURE_SVM) || kvm_cpu_has(X86_FEATURE_VMX);
+	uint64_t host_aperf_before, host_mperf_before;
+	vm_vaddr_t nested_test_data_gva;
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	int msr_fd, cpu, i;
+
+	/* Sanity check that APERF/MPERF are unsupported by default. */
+	vm = vm_create_with_one_vcpu(&vcpu, guest_no_aperfmperf);
+	vcpu_run(vcpu);
+	TEST_ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_DONE);
+	kvm_vm_free(vm);
+
+	cpu = pin_self_to_any_cpu();
+
+	msr_fd = open_dev_msr(cpu);
+
+	/*
+	 * This test requires a non-standard VM initialization, because
+	 * KVM_ENABLE_CAP cannot be used on a VM file descriptor after
+	 * a VCPU has been created.
+	 */
+	vm = vm_create(1);
+
+	TEST_REQUIRE(vm_check_cap(vm, KVM_CAP_X86_DISABLE_EXITS) &
+		     KVM_X86_DISABLE_EXITS_APERFMPERF);
+
+	vm_enable_cap(vm, KVM_CAP_X86_DISABLE_EXITS,
+		      KVM_X86_DISABLE_EXITS_APERFMPERF);
+
+	vcpu = vm_vcpu_add(vm, 0, guest_code);
+
+	if (!has_nested)
+		nested_test_data_gva = NONCANONICAL;
+	else if (kvm_cpu_has(X86_FEATURE_SVM))
+		vcpu_alloc_svm(vm, &nested_test_data_gva);
+	else
+		vcpu_alloc_vmx(vm, &nested_test_data_gva);
+
+	vcpu_args_set(vcpu, 1, nested_test_data_gva);
+
+	host_aperf_before = read_dev_msr(msr_fd, MSR_IA32_APERF);
+	host_mperf_before = read_dev_msr(msr_fd, MSR_IA32_MPERF);
+
+	for (i = 0; i <= NUM_ITERATIONS * (1 + has_nested); i++) {
+		uint64_t host_aperf_after, host_mperf_after;
+		uint64_t guest_aperf, guest_mperf;
+		struct ucall uc;
+
+		vcpu_run(vcpu);
+		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_DONE:
+			goto done;
+		case UCALL_ABORT:
+			REPORT_GUEST_ASSERT(uc);
+		case UCALL_SYNC:
+			guest_aperf = uc.args[0];
+			guest_mperf = uc.args[1];
+
+			host_aperf_after = read_dev_msr(msr_fd, MSR_IA32_APERF);
+			host_mperf_after = read_dev_msr(msr_fd, MSR_IA32_MPERF);
+
+			TEST_ASSERT(host_aperf_before < guest_aperf,
+				    "APERF: host_before (0x%" PRIx64 ") >= guest (0x%" PRIx64 ")",
+				    host_aperf_before, guest_aperf);
+			TEST_ASSERT(guest_aperf < host_aperf_after,
+				    "APERF: guest (0x%" PRIx64 ") >= host_after (0x%" PRIx64 ")",
+				    guest_aperf, host_aperf_after);
+			TEST_ASSERT(host_mperf_before < guest_mperf,
+				    "MPERF: host_before (0x%" PRIx64 ") >= guest (0x%" PRIx64 ")",
+				    host_mperf_before, guest_mperf);
+			TEST_ASSERT(guest_mperf < host_mperf_after,
+				    "MPERF: guest (0x%" PRIx64 ") >= host_after (0x%" PRIx64 ")",
+				    guest_mperf, host_mperf_after);
+
+			host_aperf_before = host_aperf_after;
+			host_mperf_before = host_mperf_after;
+
+			break;
+		}
+	}
+	TEST_FAIL("Didn't receive UCALL_DONE\n");
+done:
+	kvm_vm_free(vm);
+	close(msr_fd);
+
+	return 0;
+}