KVM: selftests: Test disabling NX hugepages on a VM

Add an argument to the NX huge pages test to test disabling the feature
on a VM using the new capability.
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220613212523.3436117-10-bgardon@google.com>
[Handle failure of sudo or setcap more gracefully. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/include/kvm_util_base.h

@@ -809,4 +809,10 @@ static inline void virt_dump(FILE *stream, struct kvm_vm *vm, uint8_t indent)
 	virt_arch_dump(stream, vm, indent);
 }
 
+
+static inline int __vm_disable_nx_huge_pages(struct kvm_vm *vm)
+{
+	return __vm_enable_cap(vm, KVM_CAP_VM_DISABLE_NX_HUGE_PAGES, 0);
+}
+
 #endif /* SELFTEST_KVM_UTIL_BASE_H */

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

@@ -107,53 +107,34 @@ static void wait_for_reclaim(int reclaim_period_ms)
 	nanosleep(&ts, NULL);
 }
 
-static void help(char *name)
-{
-	puts("");
-	printf("usage: %s [-h] [-p period_ms] [-t token]\n", name);
-	puts("");
-	printf(" -p: The NX reclaim period in miliseconds.\n");
-	printf(" -t: The magic token to indicate environment setup is done.\n");
-	puts("");
-	exit(0);
-}
-
-int main(int argc, char **argv)
+void run_test(int reclaim_period_ms, bool disable_nx_huge_pages,
+	      bool reboot_permissions)
 {
-	int reclaim_period_ms = 0, token = 0, opt;
 	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
 	void *hva;
+	int r;
 
-	while ((opt = getopt(argc, argv, "hp:t:")) != -1) {
-		switch (opt) {
-		case 'p':
-			reclaim_period_ms = atoi(optarg);
-			break;
-		case 't':
-			token = atoi(optarg);
-			break;
-		case 'h':
-		default:
-			help(argv[0]);
-			break;
-		}
-	}
-
-	if (token != MAGIC_TOKEN) {
-		print_skip("This test must be run with the magic token %d.\n"
-			   "This is done by nx_huge_pages_test.sh, which\n"
-			   "also handles environment setup for the test.",
-			   MAGIC_TOKEN);
-		exit(KSFT_SKIP);
-	}
+	vm = vm_create(1);
 
-	if (!reclaim_period_ms) {
-		print_skip("The NX reclaim period must be specified and non-zero");
-		exit(KSFT_SKIP);
+	if (disable_nx_huge_pages) {
+		/*
+		 * Cannot run the test without NX huge pages if the kernel
+		 * does not support it.
+		 */
+		if (!kvm_check_cap(KVM_CAP_VM_DISABLE_NX_HUGE_PAGES))
+			return;
+
+		r = __vm_disable_nx_huge_pages(vm);
+		if (reboot_permissions) {
+			TEST_ASSERT(!r, "Disabling NX huge pages should succeed if process has reboot permissions");
+		} else {
+			TEST_ASSERT(r == -1 && errno == EPERM,
+				    "This process should not have permission to disable NX huge pages");
+			return;
+		}
 	}
 
-	vm = vm_create(1);
 	vcpu = vm_vcpu_add(vm, 0, guest_code);
 
 	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS_HUGETLB,
@@ -187,31 +168,38 @@ int main(int argc, char **argv)
 	/*
 	 * Next, the guest will execute from the first huge page, causing it
 	 * to be remapped at 4k.
+	 *
+	 * If NX huge pages are disabled, this should have no effect.
 	 */
 	vcpu_run(vcpu);
-	check_2m_page_count(vm, 1);
-	check_split_count(vm, 1);
+	check_2m_page_count(vm, disable_nx_huge_pages ? 2 : 1);
+	check_split_count(vm, disable_nx_huge_pages ? 0 : 1);
 
 	/*
 	 * Executing from the third huge page (previously unaccessed) will
 	 * cause part to be mapped at 4k.
+	 *
+	 * If NX huge pages are disabled, it should be mapped at 2M.
 	 */
 	vcpu_run(vcpu);
-	check_2m_page_count(vm, 1);
-	check_split_count(vm, 2);
+	check_2m_page_count(vm, disable_nx_huge_pages ? 3 : 1);
+	check_split_count(vm, disable_nx_huge_pages ? 0 : 2);
 
 	/* Reading from the first huge page again should have no effect. */
 	vcpu_run(vcpu);
-	check_2m_page_count(vm, 1);
-	check_split_count(vm, 2);
+	check_2m_page_count(vm, disable_nx_huge_pages ? 3 : 1);
+	check_split_count(vm, disable_nx_huge_pages ? 0 : 2);
 
 	/* Give recovery thread time to run. */
 	wait_for_reclaim(reclaim_period_ms);
 
 	/*
 	 * Now that the reclaimer has run, all the split pages should be gone.
+	 *
+	 * If NX huge pages are disabled, the relaimer will not run, so
+	 * nothing should change from here on.
 	 */
-	check_2m_page_count(vm, 1);
+	check_2m_page_count(vm, disable_nx_huge_pages ? 3 : 1);
 	check_split_count(vm, 0);
 
 	/*
@@ -219,10 +207,62 @@ int main(int argc, char **argv)
 	 * reading from it causes a huge page mapping to be installed.
 	 */
 	vcpu_run(vcpu);
-	check_2m_page_count(vm, 2);
+	check_2m_page_count(vm, disable_nx_huge_pages ? 3 : 2);
 	check_split_count(vm, 0);
 
 	kvm_vm_free(vm);
+}
+
+static void help(char *name)
+{
+	puts("");
+	printf("usage: %s [-h] [-p period_ms] [-t token]\n", name);
+	puts("");
+	printf(" -p: The NX reclaim period in miliseconds.\n");
+	printf(" -t: The magic token to indicate environment setup is done.\n");
+	printf(" -r: The test has reboot permissions and can disable NX huge pages.\n");
+	puts("");
+	exit(0);
+}
+
+int main(int argc, char **argv)
+{
+	int reclaim_period_ms = 0, token = 0, opt;
+	bool reboot_permissions = false;
+
+	while ((opt = getopt(argc, argv, "hp:t:r")) != -1) {
+		switch (opt) {
+		case 'p':
+			reclaim_period_ms = atoi(optarg);
+			break;
+		case 't':
+			token = atoi(optarg);
+			break;
+		case 'r':
+			reboot_permissions = true;
+			break;
+		case 'h':
+		default:
+			help(argv[0]);
+			break;
+		}
+	}
+
+	if (token != MAGIC_TOKEN) {
+		print_skip("This test must be run with the magic token %d.\n"
+			   "This is done by nx_huge_pages_test.sh, which\n"
+			   "also handles environment setup for the test.",
+			   MAGIC_TOKEN);
+		exit(KSFT_SKIP);
+	}
+
+	if (!reclaim_period_ms) {
+		print_skip("The NX reclaim period must be specified and non-zero");
+		exit(KSFT_SKIP);
+	}
+
+	run_test(reclaim_period_ms, false, reboot_permissions);
+	run_test(reclaim_period_ms, true, reboot_permissions);
 
 	return 0;
 }

tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh

@@ -20,6 +20,10 @@ function sudo_echo () {
 	echo "$1" | sudo tee -a "$2" > /dev/null
 }
 
+NXECUTABLE="$(dirname $0)/nx_huge_pages_test"
+
+sudo_echo test /dev/null || exit 4 # KSFT_SKIP=4
+
 (
 	set -e
 
@@ -28,7 +32,22 @@ function sudo_echo () {
 	sudo_echo 100 /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms
 	sudo_echo "$(( $HUGE_PAGES + 3 ))" /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
 
-	"$(dirname $0)"/nx_huge_pages_test -t 887563923 -p 100
+	# Test with reboot permissions
+	if [ $(whoami) == "root" ] || sudo setcap cap_sys_boot+ep $NXECUTABLE 2> /dev/null; then
+		echo Running test with CAP_SYS_BOOT enabled
+		$NXECUTABLE -t 887563923 -p 100 -r
+		test $(whoami) == "root" || sudo setcap cap_sys_boot-ep $NXECUTABLE
+	else
+		echo setcap failed, skipping nx_huge_pages_test with CAP_SYS_BOOT enabled
+	fi
+
+	# Test without reboot permissions
+	if [ $(whoami) != "root" ] ; then
+		echo Running test with CAP_SYS_BOOT disabled
+		$NXECUTABLE -t 887563923 -p 100
+	else
+		echo Running as root, skipping nx_huge_pages_test with CAP_SYS_BOOT disabled
+	fi
 )
 RET=$?