Enable hypervisor on pKVM builds

gs101 builds are getting experimental support for pKVM which can be
enabled either using fastboot or with misc_writer. For _pkvm builds we
want the device to automatically enable pKVM for testing. This patch
adds a new early-init service which checks for the presence of /dev/kvm
and if not found, writes to /misc and forces a reboot.

Bug: 192819132
Bug: 202484976
Test: flash a _pkvm build, observe double-reboot, check /dev/kvm exists
Change-Id: I3834b3e4c6118b3f6e4093ce52d5b94117eca29c

device.mk

@@ -1071,6 +1071,7 @@ PRODUCT_PACKAGES += \
 ifeq ($(TARGET_PKVM_ENABLED),true)
     $(call inherit-product, packages/modules/Virtualization/apex/product_packages.mk)
     PRODUCT_BUILD_PVMFW_IMAGE := true
+    PRODUCT_PACKAGES += pkvm_enabler
 endif
 
 # Enable watchdog timeout loop breaker.

pkvm/Android.bp

@@ -0,0 +1,31 @@
+// Copyright (C) 2021 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package {
+    // See: http://go/android-license-faq
+    // A large-scale-change added 'default_applicable_licenses' to import
+    // all of the 'license_kinds' from "//device/google/gs101:device_google_gs101_license"
+    // to get the below license kinds:
+    //   SPDX-license-identifier-Apache-2.0
+    default_applicable_licenses: [
+        "//device/google/gs101:device_google_gs101_license",
+    ],
+}
+
+cc_binary {
+    name: "pkvm_enabler",
+    vendor: true,
+    init_rc: ["pkvm_enabler.gs101.rc"],
+    srcs: ["pkvm_enabler.c"],
+    shared_libs: ["liblog"],
+}

pkvm/pkvm_enabler.c

@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG     "pkvm_enabler"
+
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <log/log.h>
+
+#define KVM_DEVICE  "/dev/kvm"
+#define MISC_WRITER "/vendor/bin/misc_writer"
+
+int main() {
+    char *newargv[] = { MISC_WRITER, "--set-enable-pkvm", NULL };
+    char *newenvp[] = { NULL };
+    pid_t pid;
+    int ret, wstatus;
+
+    /* Check whether KVM device exists. */
+    ret = access(KVM_DEVICE, F_OK);
+
+    /* If KVM device exists, return SUCCESS to continue booting. */
+    if (ret == 0) {
+        exit(EXIT_SUCCESS);
+    }
+
+    if (ret != -ENOENT) {
+        ALOGW("Unexpected error from access(): %d", ret);
+    }
+
+    /*
+     * If KVM device does not exist, run misc_writer and return FAILURE
+     * to force a reboot.
+     */
+    pid = fork();
+    if (pid == -1) {
+        ALOGE("Could not fork: %d", errno);
+        exit(EXIT_FAILURE);
+    }
+
+    if (pid == 0) {
+        execve(MISC_WRITER, newargv, newenvp);
+        ALOGE("Could not execute " MISC_WRITER ": %d", errno);
+        _exit(EXIT_FAILURE);
+    }
+
+    waitpid(pid, &wstatus, 0);
+    if (WIFEXITED(wstatus)) {
+        ret = WEXITSTATUS(wstatus);
+        if (ret) {
+            ALOGE(MISC_WRITER " exit status: %d", ret);
+        }
+    } else {
+        ALOGE(MISC_WRITER " terminated unexpectedly: %d", wstatus);
+    }
+
+    exit(EXIT_FAILURE);
+}

pkvm/pkvm_enabler.gs101.rc

@@ -0,0 +1,5 @@
+service pkvm_enabler /vendor/bin/pkvm_enabler
+    reboot_on_failure reboot,pkvm-not-enabled
+
+on early-init
+    exec_start pkvm_enabler