kvm: selftests: add cr4_cpuid_sync_test

KVM is supposed to update some guest VM's CPUID bits (e.g. OSXSAVE) when
CR4 is changed. A bug was found in KVM recently and it was fixed by
Commit c4d2188206 ("KVM: x86: Update cpuid properly when CR4.OSXAVE or
CR4.PKE is changed"). This patch adds a test to verify the synchronization
between guest VM's CR4 and CPUID bits.

Signed-off-by: Wei Huang <wei@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/.gitignore

@@ -1,3 +1,4 @@
+cr4_cpuid_sync_test
 set_sregs_test
 sync_regs_test
 vmx_tsc_adjust_test

tools/testing/selftests/kvm/Makefile

@@ -9,6 +9,7 @@ LIBKVM_x86_64 = lib/x86.c lib/vmx.c
 TEST_GEN_PROGS_x86_64 = set_sregs_test
 TEST_GEN_PROGS_x86_64 += sync_regs_test
 TEST_GEN_PROGS_x86_64 += vmx_tsc_adjust_test
+TEST_GEN_PROGS_x86_64 += cr4_cpuid_sync_test
 
 TEST_GEN_PROGS += $(TEST_GEN_PROGS_$(UNAME_M))
 LIBKVM += $(LIBKVM_$(UNAME_M))

tools/testing/selftests/kvm/cr4_cpuid_sync_test.c

@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * CR4 and CPUID sync test
+ *
+ * Copyright 2018, Red Hat, Inc. and/or its affiliates.
+ *
+ * Author:
+ *   Wei Huang <wei@redhat.com>
+ */
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+#include "test_util.h"
+
+#include "kvm_util.h"
+#include "x86.h"
+
+#define X86_FEATURE_XSAVE	(1<<26)
+#define X86_FEATURE_OSXSAVE	(1<<27)
+#define VCPU_ID			1
+
+enum {
+	GUEST_UPDATE_CR4 = 0x1000,
+	GUEST_FAILED,
+	GUEST_DONE,
+};
+
+static void exit_to_hv(uint16_t port)
+{
+	__asm__ __volatile__("in %[port], %%al"
+			     :
+			     : [port]"d"(port)
+			     : "rax");
+}
+
+static inline bool cr4_cpuid_is_sync(void)
+{
+	int func, subfunc;
+	uint32_t eax, ebx, ecx, edx;
+	uint64_t cr4;
+
+	func = 0x1;
+	subfunc = 0x0;
+	__asm__ __volatile__("cpuid"
+			     : "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx)
+			     : "a"(func), "c"(subfunc));
+
+	cr4 = get_cr4();
+
+	return (!!(ecx & X86_FEATURE_OSXSAVE)) == (!!(cr4 & X86_CR4_OSXSAVE));
+}
+
+static void guest_code(void)
+{
+	uint64_t cr4;
+
+	/* turn on CR4.OSXSAVE */
+	cr4 = get_cr4();
+	cr4 |= X86_CR4_OSXSAVE;
+	set_cr4(cr4);
+
+	/* verify CR4.OSXSAVE == CPUID.OSXSAVE */
+	if (!cr4_cpuid_is_sync())
+		exit_to_hv(GUEST_FAILED);
+
+	/* notify hypervisor to change CR4 */
+	exit_to_hv(GUEST_UPDATE_CR4);
+
+	/* check again */
+	if (!cr4_cpuid_is_sync())
+		exit_to_hv(GUEST_FAILED);
+
+	exit_to_hv(GUEST_DONE);
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_run *run;
+	struct kvm_vm *vm;
+	struct kvm_sregs sregs;
+	struct kvm_cpuid_entry2 *entry;
+	int rc;
+
+	entry = kvm_get_supported_cpuid_entry(1);
+	if (!(entry->ecx & X86_FEATURE_XSAVE)) {
+		printf("XSAVE feature not supported, skipping test\n");
+		return 0;
+	}
+
+	/* Tell stdout not to buffer its content */
+	setbuf(stdout, NULL);
+
+	/* Create VM */
+	vm = vm_create_default(VCPU_ID, guest_code);
+	vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
+	run = vcpu_state(vm, VCPU_ID);
+
+	while (1) {
+		rc = _vcpu_run(vm, VCPU_ID);
+
+		if (run->exit_reason == KVM_EXIT_IO) {
+			switch (run->io.port) {
+			case GUEST_UPDATE_CR4:
+				/* emulate hypervisor clearing CR4.OSXSAVE */
+				vcpu_sregs_get(vm, VCPU_ID, &sregs);
+				sregs.cr4 &= ~X86_CR4_OSXSAVE;
+				vcpu_sregs_set(vm, VCPU_ID, &sregs);
+				break;
+			case GUEST_FAILED:
+				TEST_ASSERT(false, "Guest CR4 bit (OSXSAVE) unsynchronized with CPUID bit.");
+				break;
+			case GUEST_DONE:
+				goto done;
+			default:
+				TEST_ASSERT(false, "Unknown port 0x%x.",
+					    run->io.port);
+			}
+		}
+	}
+
+	kvm_vm_free(vm);
+
+done:
+	return 0;
+}