KVM: selftests: Add MONITOR/MWAIT quirk test

Add a test to verify the "MONITOR/MWAIT never fault" quirk, and as a
bonus, also verify the related "MISC_ENABLES ignores ENABLE_MWAIT" quirk.

If the "never fault" quirk is enabled, MONITOR/MWAIT should always be
emulated as NOPs, even if they're reported as disabled in guest CPUID.
Use the MISC_ENABLES quirk to coerce KVM into toggling the MWAIT CPUID
enable, as KVM now disallows manually toggling CPUID bits after running
the vCPU.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220608224516.3788274-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/.gitignore

@@ -28,6 +28,7 @@
 /x86_64/max_vcpuid_cap_test
 /x86_64/mmio_warning_test
 /x86_64/mmu_role_test
+/x86_64/monitor_mwait_test
 /x86_64/platform_info_test
 /x86_64/pmu_event_filter_test
 /x86_64/set_boot_cpu_id

tools/testing/selftests/kvm/Makefile

@@ -84,6 +84,7 @@ 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/mmio_warning_test
 TEST_GEN_PROGS_x86_64 += x86_64/mmu_role_test
+TEST_GEN_PROGS_x86_64 += x86_64/monitor_mwait_test
 TEST_GEN_PROGS_x86_64 += x86_64/platform_info_test
 TEST_GEN_PROGS_x86_64 += x86_64/pmu_event_filter_test
 TEST_GEN_PROGS_x86_64 += x86_64/set_boot_cpu_id

tools/testing/selftests/kvm/x86_64/monitor_mwait_test.c

+// SPDX-License-Identifier: GPL-2.0
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+#include "kvm_util.h"
+#include "processor.h"
+
+#define X86_FEATURE_MWAIT (1u << 3)
+
+enum monitor_mwait_testcases {
+	MWAIT_QUIRK_DISABLED = BIT(0),
+	MISC_ENABLES_QUIRK_DISABLED = BIT(1),
+	MWAIT_DISABLED = BIT(2),
+};
+
+static void guest_monitor_wait(int testcase)
+{
+	/*
+	 * If both MWAIT and its quirk are disabled, MONITOR/MWAIT should #UD,
+	 * in all other scenarios KVM should emulate them as nops.
+	 */
+	bool fault_wanted = (testcase & MWAIT_QUIRK_DISABLED) &&
+			    (testcase & MWAIT_DISABLED);
+	u8 vector;
+
+	GUEST_SYNC(testcase);
+
+	vector = kvm_asm_safe("monitor");
+	if (fault_wanted)
+		GUEST_ASSERT_2(vector == UD_VECTOR, testcase, vector);
+	else
+		GUEST_ASSERT_2(!vector, testcase, vector);
+
+	vector = kvm_asm_safe("monitor");
+	if (fault_wanted)
+		GUEST_ASSERT_2(vector == UD_VECTOR, testcase, vector);
+	else
+		GUEST_ASSERT_2(!vector, testcase, vector);
+}
+
+static void guest_code(void)
+{
+	guest_monitor_wait(MWAIT_DISABLED);
+
+	guest_monitor_wait(MWAIT_QUIRK_DISABLED | MWAIT_DISABLED);
+
+	guest_monitor_wait(MISC_ENABLES_QUIRK_DISABLED | MWAIT_DISABLED);
+	guest_monitor_wait(MISC_ENABLES_QUIRK_DISABLED);
+
+	guest_monitor_wait(MISC_ENABLES_QUIRK_DISABLED | MWAIT_QUIRK_DISABLED | MWAIT_DISABLED);
+	guest_monitor_wait(MISC_ENABLES_QUIRK_DISABLED | MWAIT_QUIRK_DISABLED);
+
+	GUEST_DONE();
+}
+
+int main(int argc, char *argv[])
+{
+	uint64_t disabled_quirks;
+	struct kvm_cpuid2 *cpuid;
+	struct kvm_cpuid_entry2 *entry;
+	struct kvm_vcpu *vcpu;
+	struct kvm_run *run;
+	struct kvm_vm *vm;
+	struct ucall uc;
+	int testcase;
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_DISABLE_QUIRKS2));
+
+	cpuid = kvm_get_supported_cpuid();
+
+	entry = kvm_get_supported_cpuid_index(1, 0);
+	entry->ecx &= ~X86_FEATURE_MWAIT;
+	set_cpuid(cpuid, entry);
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+	vcpu_set_cpuid(vcpu, cpuid);
+
+	run = vcpu->run;
+
+	vm_init_descriptor_tables(vm);
+	vcpu_init_descriptor_tables(vcpu);
+
+	while (1) {
+		vcpu_run(vcpu);
+
+		TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+			    "Unexpected exit reason: %u (%s),\n",
+			    run->exit_reason,
+			    exit_reason_str(run->exit_reason));
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_SYNC:
+			testcase = uc.args[1];
+			break;
+		case UCALL_ABORT:
+			TEST_FAIL("%s at %s:%ld, testcase = %lx, vector = %ld",
+				  (const char *)uc.args[0], __FILE__,
+				  uc.args[1], uc.args[2], uc.args[3]);
+			goto done;
+		case UCALL_DONE:
+			goto done;
+		default:
+			TEST_FAIL("Unknown ucall %lu", uc.cmd);
+			goto done;
+		}
+
+		disabled_quirks = 0;
+		if (testcase & MWAIT_QUIRK_DISABLED)
+			disabled_quirks |= KVM_X86_QUIRK_MWAIT_NEVER_FAULTS;
+		if (testcase & MISC_ENABLES_QUIRK_DISABLED)
+			disabled_quirks |= KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT;
+		vm_enable_cap(vm, KVM_CAP_DISABLE_QUIRKS2, disabled_quirks);
+
+		/*
+		 * If the MISC_ENABLES quirk (KVM neglects to update CPUID to
+		 * enable/disable MWAIT) is disabled, toggle the ENABLE_MWAIT
+		 * bit in MISC_ENABLES accordingly.  If the quirk is enabled,
+		 * the only valid configuration is MWAIT disabled, as CPUID
+		 * can't be manually changed after running the vCPU.
+		 */
+		if (!(testcase & MISC_ENABLES_QUIRK_DISABLED)) {
+			TEST_ASSERT(testcase & MWAIT_DISABLED,
+				    "Can't toggle CPUID features after running vCPU");
+			continue;
+		}
+
+		vcpu_set_msr(vcpu, MSR_IA32_MISC_ENABLE,
+			     (testcase & MWAIT_DISABLED) ? 0 : MSR_IA32_MISC_ENABLE_MWAIT);
+	}
+
+done:
+	kvm_vm_free(vm);
+	return 0;
+}