misc: Upgrade to use the vm-memory crate w/ dirty-page-tracking

As the first step to complete live-migration with tracking dirty-pages
written by the VMM, this commit patches the dependent vm-memory crate to
the upstream version with the dirty-page-tracking capability. Most
changes are due to the updated `GuestMemoryMmap`, `GuestRegionMmap`, and
`MmapRegion` structs which are taking an additional generic type
parameter to specify what 'bitmap backend' is used.

The above changes should be transparent to the rest of the code base,
e.g. all unit/integration tests should pass without additional changes.

Signed-off-by: Bo Chen <chen.bo@intel.com>

Cargo.lock

@@ -1228,8 +1228,7 @@ source = "git+https://github.com/rust-vmm/vm-fdt?branch=master#956b5a5ea1d7b9202
 [[package]]
 name = "vm-memory"
 version = "0.5.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "625f401b1b8b3ac3d43f53903cd138cfe840bd985f8581e553027b31d2bb8ae8"
+source = "git+https://github.com/rust-vmm/vm-memory?rev=5bd7138758183a73ac0da27ce40c004d95f1a7e9#5bd7138758183a73ac0da27ce40c004d95f1a7e9"
 dependencies = [
  "arc-swap",
  "libc",

Cargo.toml

@@ -37,6 +37,7 @@ clap = { version = "2.33.3", features = ["wrap_help"] }
 [patch.crates-io]
 kvm-bindings = { git = "https://github.com/cloud-hypervisor/kvm-bindings", branch = "ch-v0.4.0", features = ["with-serde", "fam-wrappers"] }
 versionize_derive = { git = "https://github.com/cloud-hypervisor/versionize_derive", branch = "ch" }
+vm-memory = { git = "https://github.com/rust-vmm/vm-memory", rev = "5bd7138758183a73ac0da27ce40c004d95f1a7e9"}
 
 [dev-dependencies]
 credibility = "0.1.3"

arch/Cargo.toml

@@ -22,6 +22,6 @@ thiserror = "1.0"
 versionize = "0.1.6"
 versionize_derive = "0.1.4"
 vm-fdt = { git = "https://github.com/rust-vmm/vm-fdt", branch = "master" }
-vm-memory = { version = "0.5.0", features = ["backend-mmap"] }
+vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-bitmap"] }
 vm-migration = { path = "../vm-migration" }
 

arch/src/aarch64/fdt.rs

@@ -12,6 +12,7 @@ use std::fmt::Debug;
 use std::result;
 
 use super::super::DeviceType;
+use super::super::GuestMemoryMmap;
 use super::super::InitramfsConfig;
 use super::get_fdt_addr;
 use super::gic::GicDevice;
@@ -20,7 +21,7 @@ use super::layout::{
     PCI_MMCONFIG_START,
 };
 use vm_fdt::{FdtWriter, FdtWriterResult};
-use vm_memory::{Address, Bytes, GuestAddress, GuestMemory, GuestMemoryError, GuestMemoryMmap};
+use vm_memory::{Address, Bytes, GuestAddress, GuestMemory, GuestMemoryError};
 
 // This is a value for uniquely identifying the FDT node declaring the interrupt controller.
 const GIC_PHANDLE: u32 = 1;

arch/src/aarch64/mod.rs

@@ -13,6 +13,7 @@ pub mod regs;
 
 pub use self::fdt::DeviceInfoForFdt;
 use crate::DeviceType;
+use crate::GuestMemoryMmap;
 use crate::RegionType;
 use gic::GicDevice;
 use std::collections::HashMap;
@@ -20,8 +21,7 @@ use std::ffi::CStr;
 use std::fmt::Debug;
 use std::sync::Arc;
 use vm_memory::{
-    Address, GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryAtomic, GuestMemoryMmap,
-    GuestUsize,
+    Address, GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryAtomic, GuestUsize,
 };
 
 /// Errors thrown while configuring aarch64 system.

arch/src/aarch64/regs.rs

@@ -6,13 +6,13 @@
 // found in the THIRD-PARTY file.
 
 use super::get_fdt_addr;
+use crate::GuestMemoryMmap;
 use hypervisor::kvm::kvm_bindings::{
     kvm_regs, user_pt_regs, KVM_REG_ARM64, KVM_REG_ARM_CORE, KVM_REG_SIZE_U64,
 };
 use hypervisor::{arm64_core_reg_id, offset__of};
 use std::sync::Arc;
 use std::{mem, result};
-use vm_memory::GuestMemoryMmap;
 
 /// Errors thrown while setting aarch64 registers.
 #[derive(Debug)]

arch/src/lib.rs

@@ -14,6 +14,8 @@ extern crate log;
 use std::fmt;
 use std::result;
 
+type GuestMemoryMmap = vm_memory::GuestMemoryMmap<vm_memory::bitmap::AtomicBitmap>;
+
 /// Type for returning error code.
 #[derive(Debug)]
 pub enum Error {

arch/src/x86_64/mod.rs

@@ -12,6 +12,7 @@ pub mod layout;
 mod mpspec;
 mod mptable;
 pub mod regs;
+use crate::GuestMemoryMmap;
 use crate::InitramfsConfig;
 use crate::RegionType;
 use hypervisor::{CpuId, CpuIdEntry, CPUID_FLAG_VALID_INDEX};
@@ -22,7 +23,7 @@ use linux_loader::loader::elf::start_info::{
 use std::mem;
 use vm_memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryAtomic,
-    GuestMemoryMmap, GuestMemoryRegion, GuestUsize,
+    GuestMemoryRegion, GuestUsize,
 };
 mod smbios;
 use std::arch::x86_64;

arch/src/x86_64/mptable.rs

@@ -7,14 +7,13 @@
 
 use crate::layout::{APIC_START, HIGH_RAM_START, IOAPIC_START};
 use crate::x86_64::mpspec;
+use crate::GuestMemoryMmap;
 use libc::c_char;
 use std::io;
 use std::mem;
 use std::result;
 use std::slice;
-use vm_memory::{
-    Address, ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryError, GuestMemoryMmap,
-};
+use vm_memory::{Address, ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryError};
 
 // This is a workaround to the Rust enforcement specifying that any implementation of a foreign
 // trait (in this case `ByteValued`) where:

arch/src/x86_64/regs.rs

@@ -7,12 +7,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE-BSD-3-Clause file.
 use crate::layout::{BOOT_GDT_START, BOOT_IDT_START, PVH_INFO_START};
+use crate::GuestMemoryMmap;
 use hypervisor::arch::x86::gdt::{gdt_entry, segment_from_gdt};
 use hypervisor::arch::x86::regs::*;
 use hypervisor::x86_64::{FpuState, SpecialRegisters, StandardRegisters};
 use std::sync::Arc;
 use std::{mem, result};
-use vm_memory::{Address, Bytes, GuestMemory, GuestMemoryError, GuestMemoryMmap};
+use vm_memory::{Address, Bytes, GuestMemory, GuestMemoryError};
 
 #[derive(Debug)]
 pub enum Error {
@@ -163,7 +164,8 @@ pub fn configure_segments_and_sregs(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use vm_memory::{GuestAddress, GuestMemoryMmap};
+    use crate::GuestMemoryMmap;
+    use vm_memory::GuestAddress;
 
     fn create_guest_mem() -> GuestMemoryMmap {
         GuestMemoryMmap::from_ranges(&[(GuestAddress(0), 0x10000)]).unwrap()

arch/src/x86_64/smbios.rs

@@ -7,12 +7,13 @@
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
 use crate::layout::SMBIOS_START;
+use crate::GuestMemoryMmap;
 use std::fmt::{self, Display};
 use std::mem;
 use std::result;
 use std::slice;
 use vm_memory::ByteValued;
-use vm_memory::{Address, Bytes, GuestAddress, GuestMemoryMmap};
+use vm_memory::{Address, Bytes, GuestAddress};
 
 #[allow(unused_variables)]
 #[derive(Debug)]

arch/src/x86_64/tdx/mod.rs

@@ -1,10 +1,11 @@
 // Copyright © 2021 Intel Corporation
 //
 // SPDX-License-Identifier: Apache-2.0
+use crate::GuestMemoryMmap;
 use std::fs::File;
 use std::io::{Read, Seek, SeekFrom};
 use thiserror::Error;
-use vm_memory::{ByteValued, Bytes, GuestAddress, GuestMemoryError, GuestMemoryMmap};
+use vm_memory::{ByteValued, Bytes, GuestAddress, GuestMemoryError};
 
 #[derive(Error, Debug)]
 pub enum TdvfError {

block_util/Cargo.toml

@@ -17,7 +17,7 @@ thiserror = "1.0"
 versionize = "0.1.6"
 versionize_derive = "0.1.4"
 virtio-bindings = { version = "0.1", features = ["virtio-v5_0_0"]}
-vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic"] }
+vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic", "backend-bitmap"] }
 vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = ">=0.3.1"
 

block_util/src/lib.rs

@@ -35,10 +35,14 @@ use std::sync::{Arc, Mutex};
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
 use virtio_bindings::bindings::virtio_blk::*;
-use vm_memory::{ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryError, GuestMemoryMmap};
+use vm_memory::{
+    bitmap::AtomicBitmap, ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryError,
+};
 use vm_virtio::DescriptorChain;
 use vmm_sys_util::eventfd::EventFd;
 
+type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;
+
 const SECTOR_SHIFT: u8 = 9;
 pub const SECTOR_SIZE: u64 = 0x01 << SECTOR_SHIFT;
 

net_util/Cargo.toml

@@ -14,7 +14,7 @@ serde = "1.0.126"
 versionize = "0.1.6"
 versionize_derive = "0.1.4"
 virtio-bindings = "0.1.0"
-vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic"] }
+vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic", "backend-bitmap"] }
 vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = ">=0.3.1"
 

net_util/src/ctrl_queue.rs

@@ -2,6 +2,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
+use crate::GuestMemoryMmap;
 use crate::Tap;
 use libc::c_uint;
 use virtio_bindings::bindings::virtio_net::{
@@ -11,7 +12,7 @@ use virtio_bindings::bindings::virtio_net::{
     VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6,
     VIRTIO_NET_F_GUEST_UFO, VIRTIO_NET_OK,
 };
-use vm_memory::{ByteValued, Bytes, GuestMemoryError, GuestMemoryMmap};
+use vm_memory::{ByteValued, Bytes, GuestMemoryError};
 use vm_virtio::Queue;
 
 #[derive(Debug)]

net_util/src/lib.rs

@@ -30,7 +30,9 @@ use virtio_bindings::bindings::virtio_net::{
     VIRTIO_NET_F_GUEST_CSUM, VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_TSO4,
     VIRTIO_NET_F_GUEST_TSO6, VIRTIO_NET_F_GUEST_UFO, VIRTIO_NET_F_MAC, VIRTIO_NET_F_MQ,
 };
-use vm_memory::ByteValued;
+use vm_memory::{bitmap::AtomicBitmap, ByteValued};
+
+type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;
 
 pub use ctrl_queue::{CtrlQueue, Error as CtrlQueueError};
 pub use mac::{MacAddr, MAC_ADDR_LEN};

net_util/src/queue_pair.rs

@@ -3,13 +3,14 @@
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
 use super::{unregister_listener, vnet_hdr_len, Tap};
+use crate::GuestMemoryMmap;
 use rate_limiter::{RateLimiter, TokenType};
 use std::io;
 use std::num::Wrapping;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::Arc;
-use vm_memory::{Bytes, GuestAddressSpace, GuestMemory, GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{Bytes, GuestAddressSpace, GuestMemory, GuestMemoryAtomic};
 use vm_virtio::Queue;
 
 #[derive(Clone)]

vhost_user_backend/Cargo.toml

@@ -12,7 +12,7 @@ epoll = ">=4.0.1"
 libc = "0.2.95"
 log = "0.4.14"
 virtio-bindings = "0.1.0"
-vm-memory = "0.5.0"
+vm-memory = { version = "0.5.0", features = ["backend-bitmap"] }
 vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = ">=0.3.1"
 vhost = { git = "https://github.com/rust-vmm/vhost", branch = "master", package = "vhost", features = ["vhost-user-slave"] }

vhost_user_backend/src/lib.rs

@@ -27,10 +27,13 @@ use vhost::vhost_user::{
 };
 use virtio_bindings::bindings::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
 use vm_memory::guest_memory::FileOffset;
-use vm_memory::{GuestAddress, GuestMemoryMmap, GuestRegionMmap, MmapRegion};
+use vm_memory::{bitmap::AtomicBitmap, GuestAddress, MmapRegion};
 use vm_virtio::Queue;
 use vmm_sys_util::eventfd::EventFd;
 
+pub type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;
+pub type GuestRegionMmap = vm_memory::GuestRegionMmap<AtomicBitmap>;
+
 const MAX_MEM_SLOTS: u64 = 32;
 
 #[derive(Debug)]

vhost_user_block/src/lib.rs

@@ -30,11 +30,11 @@ use std::vec::Vec;
 use std::{convert, error, fmt, io};
 use vhost::vhost_user::message::*;
 use vhost::vhost_user::Listener;
-use vhost_user_backend::{VhostUserBackend, VhostUserDaemon, Vring};
+use vhost_user_backend::{GuestMemoryMmap, VhostUserBackend, VhostUserDaemon, Vring};
 use virtio_bindings::bindings::virtio_blk::*;
 use virtio_bindings::bindings::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
 use vm_memory::ByteValued;
-use vm_memory::{Bytes, GuestMemoryMmap};
+use vm_memory::Bytes;
 use vmm_sys_util::eventfd::EventFd;
 
 const SECTOR_SHIFT: u8 = 9;

vhost_user_net/src/lib.rs

@@ -22,10 +22,10 @@ use std::sync::{Arc, Mutex, RwLock};
 use std::vec::Vec;
 use vhost::vhost_user::message::*;
 use vhost::vhost_user::Listener;
-use vhost_user_backend::{VhostUserBackend, VhostUserDaemon, Vring, VringWorker};
+use vhost_user_backend::{GuestMemoryMmap, VhostUserBackend, VhostUserDaemon, Vring, VringWorker};
 use virtio_bindings::bindings::virtio_net::*;
 use virtio_bindings::bindings::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
-use vm_memory::{GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::GuestMemoryAtomic;
 use vmm_sys_util::eventfd::EventFd;
 
 pub type Result<T> = std::result::Result<T, Error>;

virtio-devices/Cargo.toml

@@ -32,7 +32,7 @@ vhost = { git = "https://github.com/rust-vmm/vhost", branch = "master", package
 virtio-bindings = { version = "0.1", features = ["virtio-v5_0_0"]}
 vm-allocator = { path = "../vm-allocator" }
 vm-device = { path = "../vm-device" }
-vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic"] }
+vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic", "backend-bitmap"] }
 vm-migration = { path = "../vm-migration" }
 vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = ">=0.3.1"

virtio-devices/src/balloon.rs

@@ -17,6 +17,7 @@ use super::{
     VirtioCommon, VirtioDevice, VirtioDeviceType, EPOLL_HELPER_EVENT_LAST, VIRTIO_F_VERSION_1,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::GuestMemoryMmap;
 use crate::{VirtioInterrupt, VirtioInterruptType};
 use libc::EFD_NONBLOCK;
 use seccomp::{SeccompAction, SeccompFilter};
@@ -31,7 +32,7 @@ use std::thread;
 use vm_memory::GuestMemory;
 use vm_memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestAddressSpace, GuestMemoryAtomic,
-    GuestMemoryError, GuestMemoryMmap,
+    GuestMemoryError,
 };
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;

virtio-devices/src/block.rs

@@ -15,6 +15,7 @@ use super::{
     EPOLL_HELPER_EVENT_LAST,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::GuestMemoryMmap;
 use crate::VirtioInterrupt;
 use block_util::{
     async_io::AsyncIo, async_io::AsyncIoError, async_io::DiskFile, build_disk_image_id, Request,
@@ -34,7 +35,7 @@ use std::{collections::HashMap, convert::TryInto};
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
 use virtio_bindings::bindings::virtio_blk::*;
-use vm_memory::{ByteValued, Bytes, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{ByteValued, Bytes, GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::VersionMapped;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;

virtio-devices/src/console.rs

@@ -8,6 +8,7 @@ use super::{
     VIRTIO_F_IOMMU_PLATFORM, VIRTIO_F_VERSION_1,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::GuestMemoryMmap;
 use crate::VirtioInterrupt;
 use libc::EFD_NONBLOCK;
 use seccomp::{SeccompAction, SeccompFilter};
@@ -23,7 +24,7 @@ use std::sync::{Arc, Barrier, Mutex};
 use std::thread;
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
-use vm_memory::{ByteValued, Bytes, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{ByteValued, Bytes, GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::VersionMapped;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;

virtio-devices/src/device.rs

@@ -7,6 +7,7 @@
 // SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause
 
 use crate::{ActivateError, ActivateResult, Error, Queue};
+use crate::{GuestMemoryMmap, GuestRegionMmap};
 use libc::EFD_NONBLOCK;
 use std::collections::HashMap;
 use std::io::Write;
@@ -16,7 +17,7 @@ use std::sync::{
     Arc, Barrier,
 };
 use std::thread;
-use vm_memory::{GuestAddress, GuestMemoryAtomic, GuestMemoryMmap, GuestRegionMmap, GuestUsize};
+use vm_memory::{GuestAddress, GuestMemoryAtomic, GuestUsize};
 use vm_migration::{MigratableError, Pausable};
 use vm_virtio::VirtioDeviceType;
 use vmm_sys_util::eventfd::EventFd;

virtio-devices/src/iommu.rs

@@ -9,6 +9,7 @@ use super::{
     EPOLL_HELPER_EVENT_LAST, VIRTIO_F_VERSION_1,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::GuestMemoryMmap;
 use crate::{DmaRemapping, VirtioInterrupt, VirtioInterruptType};
 use seccomp::{SeccompAction, SeccompFilter};
 use std::collections::BTreeMap;
@@ -26,7 +27,7 @@ use versionize_derive::Versionize;
 use vm_device::dma_mapping::ExternalDmaMapping;
 use vm_memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestAddressSpace, GuestMemoryAtomic,
-    GuestMemoryError, GuestMemoryMmap,
+    GuestMemoryError,
 };
 use vm_migration::VersionMapped;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};

virtio-devices/src/lib.rs

@@ -49,9 +49,13 @@ pub use self::pmem::*;
 pub use self::rng::*;
 pub use self::vsock::*;
 pub use self::watchdog::*;
-use vm_memory::{GuestAddress, GuestMemory};
+use vm_memory::{bitmap::AtomicBitmap, GuestAddress, GuestMemory};
 use vm_virtio::{queue::*, VirtioDeviceType};
 
+type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;
+type GuestRegionMmap = vm_memory::GuestRegionMmap<AtomicBitmap>;
+type MmapRegion = vm_memory::MmapRegion<AtomicBitmap>;
+
 const DEVICE_INIT: u32 = 0x00;
 const DEVICE_ACKNOWLEDGE: u32 = 0x01;
 const DEVICE_DRIVER: u32 = 0x02;

virtio-devices/src/mem.rs

@@ -19,6 +19,7 @@ use super::{
     EPOLL_HELPER_EVENT_LAST, VIRTIO_F_VERSION_1,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::{GuestMemoryMmap, GuestRegionMmap};
 use crate::{VirtioInterrupt, VirtioInterruptType};
 use anyhow::anyhow;
 use libc::EFD_NONBLOCK;
@@ -35,7 +36,7 @@ use std::thread;
 use vm_device::dma_mapping::ExternalDmaMapping;
 use vm_memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestAddressSpace, GuestMemoryAtomic,
-    GuestMemoryError, GuestMemoryMmap, GuestMemoryRegion, GuestRegionMmap,
+    GuestMemoryError, GuestMemoryRegion,
 };
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;

virtio-devices/src/net.rs

@@ -12,6 +12,7 @@ use super::{
     EPOLL_HELPER_EVENT_LAST,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::GuestMemoryMmap;
 use crate::VirtioInterrupt;
 use net_util::CtrlQueue;
 use net_util::{
@@ -33,7 +34,7 @@ use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
 use virtio_bindings::bindings::virtio_net::*;
 use virtio_bindings::bindings::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
-use vm_memory::{ByteValued, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{ByteValued, GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::VersionMapped;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;

virtio-devices/src/pmem.rs

@@ -13,6 +13,7 @@ use super::{
     EPOLL_HELPER_EVENT_LAST, VIRTIO_F_IOMMU_PLATFORM, VIRTIO_F_VERSION_1,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::{GuestMemoryMmap, MmapRegion};
 use crate::{VirtioInterrupt, VirtioInterruptType};
 use seccomp::{SeccompAction, SeccompFilter};
 use std::fmt::{self, Display};
@@ -28,7 +29,7 @@ use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
 use vm_memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestAddressSpace, GuestMemoryAtomic,
-    GuestMemoryError, GuestMemoryMmap, MmapRegion,
+    GuestMemoryError,
 };
 use vm_migration::VersionMapped;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};

virtio-devices/src/rng.rs

@@ -9,6 +9,7 @@ use super::{
     VIRTIO_F_VERSION_1,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::GuestMemoryMmap;
 use crate::{VirtioInterrupt, VirtioInterruptType};
 use seccomp::{SeccompAction, SeccompFilter};
 use std::fs::File;
@@ -20,7 +21,7 @@ use std::sync::{Arc, Barrier};
 use std::thread;
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
-use vm_memory::{Bytes, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{Bytes, GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::VersionMapped;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;

virtio-devices/src/transport/pci_common_config.rs

@@ -305,9 +305,10 @@ impl Snapshottable for VirtioPciCommonConfig {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::GuestMemoryMmap;
     use crate::{ActivateResult, VirtioInterrupt};
     use std::sync::Arc;
-    use vm_memory::{GuestMemoryAtomic, GuestMemoryMmap};
+    use vm_memory::GuestMemoryAtomic;
     use vmm_sys_util::eventfd::EventFd;
 
     struct DummyDevice(u32);

virtio-devices/src/transport/pci_device.rs

@@ -8,6 +8,7 @@
 
 use super::VirtioPciCommonConfig;
 use crate::transport::VirtioTransport;
+use crate::GuestMemoryMmap;
 use crate::{
     ActivateResult, Queue, VirtioDevice, VirtioDeviceType, VirtioInterrupt, VirtioInterruptType,
     DEVICE_ACKNOWLEDGE, DEVICE_DRIVER, DEVICE_DRIVER_OK, DEVICE_FAILED, DEVICE_FEATURES_OK,
@@ -35,8 +36,7 @@ use vm_device::interrupt::{
 };
 use vm_device::BusDevice;
 use vm_memory::{
-    Address, ByteValued, GuestAddress, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap,
-    GuestUsize, Le32,
+    Address, ByteValued, GuestAddress, GuestAddressSpace, GuestMemoryAtomic, GuestUsize, Le32,
 };
 use vm_migration::{
     Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable, VersionMapped,

virtio-devices/src/vhost_user/blk.rs

@@ -10,6 +10,7 @@ use super::vu_common_ctrl::{
 };
 use super::{Error, Result, DEFAULT_VIRTIO_FEATURES};
 use crate::VirtioInterrupt;
+use crate::{GuestMemoryMmap, GuestRegionMmap};
 use block_util::VirtioBlockConfig;
 use std::mem;
 use std::ops::Deref;
@@ -27,9 +28,7 @@ use virtio_bindings::bindings::virtio_blk::{
     VIRTIO_BLK_F_GEOMETRY, VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_RO, VIRTIO_BLK_F_SEG_MAX,
     VIRTIO_BLK_F_SIZE_MAX, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_WRITE_ZEROES,
 };
-use vm_memory::{
-    ByteValued, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap, GuestRegionMmap,
-};
+use vm_memory::{ByteValued, GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;
 

virtio-devices/src/vhost_user/fs.rs

@@ -12,6 +12,7 @@ use crate::{
     ActivateError, ActivateResult, Queue, UserspaceMapping, VirtioCommon, VirtioDevice,
     VirtioDeviceType, VirtioInterrupt, VirtioSharedMemoryList,
 };
+use crate::{GuestMemoryMmap, GuestRegionMmap, MmapRegion};
 use libc::{self, c_void, off64_t, pread64, pwrite64};
 use seccomp::{SeccompAction, SeccompFilter};
 use std::io;
@@ -29,7 +30,6 @@ use vhost::vhost_user::{
 };
 use vm_memory::{
     Address, ByteValued, GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryAtomic,
-    GuestMemoryMmap, GuestRegionMmap, MmapRegion,
 };
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;

virtio-devices/src/vhost_user/mod.rs

@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 use crate::{
-    EpollHelper, EpollHelperError, EpollHelperHandler, Queue, VirtioInterrupt,
+    EpollHelper, EpollHelperError, EpollHelperHandler, GuestMemoryMmap, Queue, VirtioInterrupt,
     EPOLL_HELPER_EVENT_LAST, VIRTIO_F_IN_ORDER, VIRTIO_F_NOTIFICATION_DATA,
     VIRTIO_F_ORDER_PLATFORM, VIRTIO_F_RING_EVENT_IDX, VIRTIO_F_RING_INDIRECT_DESC,
     VIRTIO_F_RING_PACKED, VIRTIO_F_VERSION_1,
@@ -14,7 +14,7 @@ use std::sync::{atomic::AtomicBool, Arc, Barrier, Mutex};
 use vhost::vhost_user::message::VhostUserVirtioFeatures;
 use vhost::vhost_user::Master;
 use vhost::Error as VhostError;
-use vm_memory::{Error as MmapError, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{Error as MmapError, GuestAddressSpace, GuestMemoryAtomic};
 use vmm_sys_util::eventfd::EventFd;
 use vu_common_ctrl::{connect_vhost_user, reinitialize_vhost_user};
 

virtio-devices/src/vhost_user/net.rs

@@ -12,6 +12,7 @@ use crate::{
     VirtioCommon, VirtioDevice, VirtioDeviceType, VirtioInterrupt, EPOLL_HELPER_EVENT_LAST,
     VIRTIO_F_RING_EVENT_IDX, VIRTIO_F_VERSION_1,
 };
+use crate::{GuestMemoryMmap, GuestRegionMmap};
 use net_util::{build_net_config_space, CtrlQueue, MacAddr, VirtioNetConfig};
 use seccomp::{SeccompAction, SeccompFilter};
 use std::ops::Deref;
@@ -29,9 +30,7 @@ use virtio_bindings::bindings::virtio_net::{
     VIRTIO_NET_F_HOST_ECN, VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_TSO6, VIRTIO_NET_F_HOST_UFO,
     VIRTIO_NET_F_MAC, VIRTIO_NET_F_MRG_RXBUF,
 };
-use vm_memory::{
-    ByteValued, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap, GuestRegionMmap,
-};
+use vm_memory::{ByteValued, GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;
 

virtio-devices/src/vhost_user/vu_common_ctrl.rs

@@ -4,6 +4,7 @@
 use super::super::{Descriptor, Queue};
 use super::{Error, Result};
 use crate::{get_host_address_range, VirtioInterrupt, VirtioInterruptType};
+use crate::{GuestMemoryMmap, GuestRegionMmap};
 use std::convert::TryInto;
 use std::os::unix::io::AsRawFd;
 use std::os::unix::net::UnixListener;
@@ -14,9 +15,7 @@ use std::vec::Vec;
 use vhost::vhost_user::message::{VhostUserProtocolFeatures, VhostUserVirtioFeatures};
 use vhost::vhost_user::{Master, VhostUserMaster};
 use vhost::{VhostBackend, VhostUserMemoryRegionInfo, VringConfigData};
-use vm_memory::{
-    Address, Error as MmapError, GuestMemory, GuestMemoryMmap, GuestMemoryRegion, GuestRegionMmap,
-};
+use vm_memory::{Address, Error as MmapError, GuestMemory, GuestMemoryRegion};
 use vmm_sys_util::eventfd::EventFd;
 
 #[derive(Debug, Clone)]

virtio-devices/src/vsock/device.rs

@@ -30,6 +30,7 @@
 use super::{VsockBackend, VsockPacket};
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
 use crate::Error as DeviceError;
+use crate::GuestMemoryMmap;
 use crate::VirtioInterrupt;
 use crate::{
     ActivateError, ActivateResult, EpollHelper, EpollHelperError, EpollHelperHandler, Queue,
@@ -47,7 +48,7 @@ use std::sync::{Arc, Barrier, RwLock};
 use std::thread;
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
-use vm_memory::{GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::{
     Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable, VersionMapped,
 };

virtio-devices/src/vsock/mod.rs

@@ -163,11 +163,12 @@ mod tests {
     use crate::device::{VirtioInterrupt, VirtioInterruptType};
     use crate::epoll_helper::EpollHelperHandler;
     use crate::EpollHelper;
+    use crate::GuestMemoryMmap;
     use libc::EFD_NONBLOCK;
     use std::os::unix::io::AsRawFd;
     use std::path::PathBuf;
     use std::sync::{Arc, RwLock};
-    use vm_memory::{GuestAddress, GuestMemoryAtomic, GuestMemoryMmap};
+    use vm_memory::{GuestAddress, GuestMemoryAtomic};
     use vm_virtio::queue::testing::VirtQueue as GuestQ;
     use vm_virtio::queue::Queue;
     use vm_virtio::queue::{VIRTQ_DESC_F_NEXT, VIRTQ_DESC_F_WRITE};

virtio-devices/src/vsock/packet.rs

@@ -342,7 +342,8 @@ mod tests {
     use super::super::tests::TestContext;
     use super::*;
     use crate::vsock::defs::MAX_PKT_BUF_SIZE;
-    use vm_memory::{GuestAddress, GuestMemoryMmap};
+    use crate::GuestMemoryMmap;
+    use vm_memory::GuestAddress;
     use vm_virtio::queue::testing::VirtqDesc as GuestQDesc;
     use vm_virtio::queue::VIRTQ_DESC_F_WRITE;
 

virtio-devices/src/watchdog.rs

@@ -11,6 +11,7 @@ use super::{
     VirtioCommon, VirtioDevice, VirtioDeviceType, EPOLL_HELPER_EVENT_LAST, VIRTIO_F_VERSION_1,
 };
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::GuestMemoryMmap;
 use crate::{VirtioInterrupt, VirtioInterruptType};
 use anyhow::anyhow;
 use seccomp::{SeccompAction, SeccompFilter};
@@ -24,7 +25,7 @@ use std::thread;
 use std::time::Instant;
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
-use vm_memory::{Bytes, GuestAddressSpace, GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::{Bytes, GuestAddressSpace, GuestMemoryAtomic};
 use vm_migration::VersionMapped;
 use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;

vm-virtio/Cargo.toml

@@ -10,4 +10,4 @@ default = []
 [dependencies]
 log = "0.4.14"
 virtio-bindings = { version = "0.1", features = ["virtio-v5_0_0"]}
-vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic"] }
+vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic", "backend-bitmap"] }

vm-virtio/src/queue.rs

@@ -16,7 +16,7 @@ use std::num::Wrapping;
 use std::sync::atomic::{fence, Ordering};
 use std::sync::Arc;
 use vm_memory::{
-    Address, ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryError, GuestMemoryMmap,
+    bitmap::AtomicBitmap, Address, ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryError,
     GuestUsize,
 };
 
@@ -24,6 +24,8 @@ pub const VIRTQ_DESC_F_NEXT: u16 = 0x1;
 pub const VIRTQ_DESC_F_WRITE: u16 = 0x2;
 pub const VIRTQ_DESC_F_INDIRECT: u16 = 0x4;
 
+type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;
+
 #[derive(Debug)]
 pub enum Error {
     GuestMemoryError,
@@ -717,7 +719,9 @@ pub mod testing {
     use std::marker::PhantomData;
     use std::mem;
     use vm_memory::Bytes;
-    use vm_memory::{Address, GuestAddress, GuestMemoryMmap, GuestUsize};
+    use vm_memory::{bitmap::AtomicBitmap, Address, GuestAddress, GuestUsize};
+
+    type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;
 
     // Represents a location in GuestMemoryMmap which holds a given type.
     pub struct SomeplaceInMemory<'a, T> {
@@ -960,7 +964,9 @@ pub mod testing {
 pub mod tests {
     use super::testing::*;
     pub use super::*;
-    use vm_memory::{GuestAddress, GuestMemoryMmap};
+    use vm_memory::{bitmap::AtomicBitmap, GuestAddress};
+
+    type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;
 
     #[test]
     fn test_checked_new_descriptor_chain() {

vmm/Cargo.toml

@@ -47,7 +47,7 @@ vfio-ioctls = { git = "https://github.com/rust-vmm/vfio-ioctls", branch = "maste
 virtio-devices = { path = "../virtio-devices" }
 vm-allocator = { path = "../vm-allocator" }
 vm-device = { path = "../vm-device" }
-vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic"] }
+vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic", "backend-bitmap"] }
 vm-migration = { path = "../vm-migration" }
 vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = { version = ">=0.5.0", features = ["with-serde"] }

vmm/src/acpi.rs

@@ -6,6 +6,7 @@ use crate::cpu::CpuManager;
 use crate::device_manager::DeviceManager;
 use crate::memory_manager::MemoryManager;
 use crate::vm::NumaNodes;
+use crate::{GuestMemoryMmap, GuestRegionMmap};
 use acpi_tables::sdt::GenericAddress;
 use acpi_tables::{aml::Aml, rsdp::Rsdp, sdt::Sdt};
 #[cfg(target_arch = "aarch64")]
@@ -15,8 +16,7 @@ use arch::DeviceType;
 
 use bitflags::bitflags;
 use std::sync::{Arc, Mutex};
-use vm_memory::GuestRegionMmap;
-use vm_memory::{Address, ByteValued, Bytes, GuestAddress, GuestMemoryMmap, GuestMemoryRegion};
+use vm_memory::{Address, ByteValued, Bytes, GuestAddress, GuestMemoryRegion};
 
 /* Values for Type in APIC sub-headers */
 #[cfg(target_arch = "x86_64")]

vmm/src/cpu.rs

@@ -19,6 +19,7 @@ use crate::memory_manager::MemoryManager;
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
 #[cfg(target_arch = "x86_64")]
 use crate::vm::physical_bits;
+use crate::GuestMemoryMmap;
 use crate::CPU_MANAGER_SNAPSHOT_ID;
 #[cfg(feature = "acpi")]
 use acpi_tables::{aml, aml::Aml, sdt::Sdt};
@@ -43,7 +44,7 @@ use std::{cmp, io, result, thread};
 use vm_device::BusDevice;
 #[cfg(feature = "acpi")]
 use vm_memory::GuestAddress;
-use vm_memory::{GuestMemoryAtomic, GuestMemoryMmap};
+use vm_memory::GuestMemoryAtomic;
 use vm_migration::{
     Migratable, MigratableError, Pausable, Snapshot, SnapshotDataSection, Snapshottable,
     Transportable,
@@ -1775,6 +1776,7 @@ mod tests {
 #[cfg(target_arch = "aarch64")]
 #[cfg(test)]
 mod tests {
+    use crate::GuestMemoryMmap;
     use arch::aarch64::layout;
     use arch::aarch64::regs::*;
     use hypervisor::kvm::aarch64::{is_system_register, MPIDR_EL1};
@@ -1784,7 +1786,7 @@ mod tests {
     };
     use hypervisor::{arm64_core_reg_id, offset__of};
     use std::mem;
-    use vm_memory::{GuestAddress, GuestMemoryMmap};
+    use vm_memory::GuestAddress;
 
     #[test]
     fn test_setup_regs() {

vmm/src/device_manager.rs

@@ -24,6 +24,7 @@ use crate::memory_manager::MEMORY_MANAGER_ACPI_SIZE;
 use crate::memory_manager::{Error as MemoryManagerError, MemoryManager};
 #[cfg(feature = "acpi")]
 use crate::vm::NumaNodes;
+use crate::GuestRegionMmap;
 use crate::PciDeviceInfo;
 use crate::{device_node, DEVICE_MANAGER_SNAPSHOT_ID};
 #[cfg(feature = "acpi")]
@@ -93,7 +94,7 @@ use vm_device::{Bus, BusDevice, Resource};
 use vm_memory::guest_memory::FileOffset;
 #[cfg(feature = "kvm")]
 use vm_memory::GuestMemoryRegion;
-use vm_memory::{Address, GuestAddress, GuestRegionMmap, GuestUsize, MmapRegion};
+use vm_memory::{Address, GuestAddress, GuestUsize, MmapRegion};
 #[cfg(feature = "cmos")]
 use vm_memory::{GuestAddressSpace, GuestMemory};
 use vm_migration::{

vmm/src/lib.rs

@@ -40,6 +40,7 @@ use std::sync::mpsc::{Receiver, RecvError, SendError, Sender};
 use std::sync::{Arc, Mutex};
 use std::{result, thread};
 use thiserror::Error;
+use vm_memory::bitmap::AtomicBitmap;
 use vm_migration::protocol::*;
 use vm_migration::{MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
 use vmm_sys_util::eventfd::EventFd;
@@ -58,6 +59,9 @@ pub mod vm;
 #[cfg(feature = "acpi")]
 mod acpi;
 
+type GuestMemoryMmap = vm_memory::GuestMemoryMmap<AtomicBitmap>;
+type GuestRegionMmap = vm_memory::GuestRegionMmap<AtomicBitmap>;
+
 /// Errors associated with VMM management
 #[derive(Debug, Error)]
 #[allow(clippy::large_enum_variant)]

vmm/src/memory_manager.rs

@@ -7,6 +7,7 @@ use crate::config::SgxEpcConfig;
 use crate::config::{HotplugMethod, MemoryConfig, MemoryZoneConfig};
 use crate::migration::url_to_path;
 use crate::MEMORY_MANAGER_SNAPSHOT_ID;
+use crate::{GuestMemoryMmap, GuestRegionMmap};
 #[cfg(feature = "acpi")]
 use acpi_tables::{aml, aml::Aml};
 use anyhow::anyhow;
@@ -36,8 +37,8 @@ use vm_device::BusDevice;
 use vm_memory::guest_memory::FileOffset;
 use vm_memory::{
     mmap::MmapRegionError, Address, Bytes, Error as MmapError, GuestAddress, GuestAddressSpace,
-    GuestMemory, GuestMemoryAtomic, GuestMemoryError, GuestMemoryLoadGuard, GuestMemoryMmap,
-    GuestMemoryRegion, GuestRegionMmap, GuestUsize, MmapRegion,
+    GuestMemory, GuestMemoryAtomic, GuestMemoryError, GuestMemoryLoadGuard, GuestMemoryRegion,
+    GuestUsize, MmapRegion,
 };
 use vm_migration::{
     protocol::{MemoryRange, MemoryRangeTable},

vmm/src/vm.rs

@@ -25,6 +25,7 @@ use crate::device_tree::DeviceTree;
 use crate::memory_manager::{Error as MemoryManagerError, MemoryManager};
 use crate::migration::{get_vm_snapshot, url_to_path, VM_SNAPSHOT_FILE};
 use crate::seccomp_filters::{get_seccomp_filter, Thread};
+use crate::{GuestMemoryMmap, GuestRegionMmap};
 use crate::{
     PciDeviceInfo, CPU_MANAGER_SNAPSHOT_ID, DEVICE_MANAGER_SNAPSHOT_ID, MEMORY_MANAGER_SNAPSHOT_ID,
 };
@@ -61,7 +62,7 @@ use std::{result, str, thread};
 use vm_device::Bus;
 use vm_memory::{
     Address, Bytes, GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryAtomic,
-    GuestMemoryMmap, GuestMemoryRegion, GuestRegionMmap,
+    GuestMemoryRegion,
 };
 use vm_migration::{
     protocol::{MemoryRange, MemoryRangeTable},
@@ -2435,11 +2436,12 @@ mod tests {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::{GuestMemoryMmap, GuestRegionMmap};
     use arch::aarch64::fdt::create_fdt;
     use arch::aarch64::gic::kvm::create_gic;
     use arch::aarch64::{layout, DeviceInfoForFdt};
     use arch::{DeviceType, MmioDeviceInfo};
-    use vm_memory::{GuestAddress, GuestMemoryMmap};
+    use vm_memory::GuestAddress;
 
     const LEN: u64 = 4096;