diff --git a/virtualizationservice/aidl/android/system/virtualizationservice/IVirtualizationService.aidl b/virtualizationservice/aidl/android/system/virtualizationservice/IVirtualizationService.aidl
index d136465..7c4b897 100644
--- a/virtualizationservice/aidl/android/system/virtualizationservice/IVirtualizationService.aidl
+++ b/virtualizationservice/aidl/android/system/virtualizationservice/IVirtualizationService.aidl
@@ -16,6 +16,7 @@
 package android.system.virtualizationservice;
 
 import android.system.virtualizationservice.IVirtualMachine;
+import android.system.virtualizationservice.PartitionType;
 import android.system.virtualizationservice.VirtualMachineConfig;
 import android.system.virtualizationservice.VirtualMachineDebugInfo;
 
@@ -32,7 +33,8 @@
      *
      * The file must be open with both read and write permissions, and should be a new empty file.
      */
-    void initializeWritablePartition(in ParcelFileDescriptor imageFd, long size);
+    void initializeWritablePartition(
+            in ParcelFileDescriptor imageFd, long size, PartitionType type);
 
     /**
      * Create or update an idsig file that digests the given APK file. The idsig file follows the
diff --git a/virtualizationservice/aidl/android/system/virtualizationservice/PartitionType.aidl b/virtualizationservice/aidl/android/system/virtualizationservice/PartitionType.aidl
new file mode 100644
index 0000000..f25e674
--- /dev/null
+++ b/virtualizationservice/aidl/android/system/virtualizationservice/PartitionType.aidl
@@ -0,0 +1,32 @@
+/*
+ * Copyright 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 android.system.virtualizationservice;
+
+/**
+ * Type of the writable partition that virtualizationservice creates via
+ * initializeWritablePartition.
+ */
+@Backing(type="int")
+enum PartitionType {
+    /**
+     * The partition is simply initialized as all zeros
+     */
+    RAW = 0,
+    /**
+     * The partition is initialized as an instance image which is formatted to hold per-VM secrets
+     */
+    ANDROID_VM_INSTANCE = 1,
+}
diff --git a/virtualizationservice/src/aidl.rs b/virtualizationservice/src/aidl.rs
index 23a9c03..ff5298c 100644
--- a/virtualizationservice/src/aidl.rs
+++ b/virtualizationservice/src/aidl.rs
@@ -32,6 +32,7 @@
     VirtualMachineRawConfig::VirtualMachineRawConfig,
 };
 use android_system_virtualizationservice::aidl::android::system::virtualizationservice::VirtualMachineDebugInfo::VirtualMachineDebugInfo;
+use android_system_virtualizationservice::aidl::android::system::virtualizationservice::PartitionType::PartitionType;
 use android_system_virtualizationservice::binder::{
     self, BinderFeatures, ExceptionCode, Interface, ParcelFileDescriptor, Status, Strong, ThreadState,
 };
@@ -43,6 +44,7 @@
 use std::convert::TryInto;
 use std::ffi::CString;
 use std::fs::{File, OpenOptions, create_dir};
+use std::io::{Error, ErrorKind, Write};
 use std::num::NonZeroU32;
 use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd};
 use std::path::{Path, PathBuf};
@@ -67,6 +69,12 @@
 /// Gaps in composite disk images are filled with a shared zero.img.
 const ZERO_FILLER_SIZE: u64 = 4096;
 
+/// Magic string for the instance image
+const ANDROID_VM_INSTANCE_MAGIC: &str = "Android-VM-instance";
+
+/// Version of the instance image format
+const ANDROID_VM_INSTANCE_VERSION: u16 = 1;
+
 /// Implementation of `IVirtualizationService`, the entry point of the AIDL service.
 #[derive(Debug, Default)]
 pub struct VirtualizationService {
@@ -190,6 +198,7 @@
         &self,
         image_fd: &ParcelFileDescriptor,
         size: i64,
+        partition_type: PartitionType,
     ) -> binder::Result<()> {
         check_manage_access()?;
         let size = size.try_into().map_err(|e| {
@@ -200,13 +209,28 @@
         })?;
         let image = clone_file(image_fd)?;
 
-        QcowFile::new(image, size).map_err(|e| {
+        let mut part = QcowFile::new(image, size).map_err(|e| {
             new_binder_exception(
                 ExceptionCode::SERVICE_SPECIFIC,
                 format!("Failed to create QCOW2 image: {}", e),
             )
         })?;
 
+        match partition_type {
+            PartitionType::RAW => Ok(()),
+            PartitionType::ANDROID_VM_INSTANCE => format_as_android_vm_instance(&mut part),
+            _ => Err(Error::new(
+                ErrorKind::Unsupported,
+                format!("Unsupported partition type {:?}", partition_type),
+            )),
+        }
+        .map_err(|e| {
+            new_binder_exception(
+                ExceptionCode::SERVICE_SPECIFIC,
+                format!("Failed to initialize partition as {:?}: {}", partition_type, e),
+            )
+        })?;
+
         Ok(())
     }
 
@@ -320,6 +344,12 @@
     Ok(())
 }
 
+fn format_as_android_vm_instance(part: &mut dyn Write) -> std::io::Result<()> {
+    part.write_all(ANDROID_VM_INSTANCE_MAGIC.as_bytes())?;
+    part.write_all(&ANDROID_VM_INSTANCE_VERSION.to_le_bytes())?;
+    part.flush()
+}
+
 /// Given the configuration for a disk image, assembles the `DiskFile` to pass to crosvm.
 ///
 /// This may involve assembling a composite disk from a set of partition images.