cloud-hypervisor/vmm/src/memory_manager.rs

// Copyright © 2019 Intel Corporation
//
// SPDX-License-Identifier: Apache-2.0
//

use crate::config::{HotplugMethod, MemoryConfig};
use crate::MEMORY_MANAGER_SNAPSHOT_ID;
#[cfg(feature = "acpi")]
use acpi_tables::{aml, aml::Aml};
use anyhow::anyhow;
use arch::{get_host_cpu_phys_bits, layout, RegionType};
#[cfg(target_arch = "x86_64")]
use devices::ioapic;
use devices::BusDevice;
use kvm_bindings::{kvm_userspace_memory_region, KVM_MEM_READONLY};
use kvm_ioctls::*;
use std::convert::TryInto;
use std::ffi;
use std::fs::{File, OpenOptions};
use std::io;
use std::os::unix::io::{FromRawFd, RawFd};
use std::path::PathBuf;
use std::result;
use std::sync::{Arc, Mutex};
use url::Url;
#[cfg(target_arch = "x86_64")]
use vm_allocator::GsiApic;
use vm_allocator::SystemAllocator;
use vm_memory::guest_memory::FileOffset;
use vm_memory::{
    mmap::MmapRegionError, Address, Bytes, Error as MmapError, GuestAddress, GuestAddressSpace,
    GuestMemory, GuestMemoryAtomic, GuestMemoryLoadGuard, GuestMemoryMmap, GuestMemoryRegion,
    GuestRegionMmap, GuestUsize, MemoryRegionAddress, MmapRegion,
};
use vm_migration::{
    Migratable, MigratableError, Pausable, Snapshot, SnapshotDataSection, Snapshottable,
    Transportable,
};

#[cfg(target_arch = "x86_64")]
const X86_64_IRQ_BASE: u32 = 5;

const HOTPLUG_COUNT: usize = 8;

#[derive(Default)]
struct HotPlugState {
    base: u64,
    length: u64,
    active: bool,
    inserting: bool,
    removing: bool,
}

pub struct MemoryManager {
    guest_memory: GuestMemoryAtomic<GuestMemoryMmap>,
    next_kvm_memory_slot: u32,
    start_of_device_area: GuestAddress,
    end_of_device_area: GuestAddress,
    fd: Arc<VmFd>,
    hotplug_slots: Vec<HotPlugState>,
    selected_slot: usize,
    backing_file: Option<PathBuf>,
    mergeable: bool,
    allocator: Arc<Mutex<SystemAllocator>>,
    hotplug_method: HotplugMethod,
    boot_ram: u64,
    current_ram: u64,
    next_hotplug_slot: usize,
    pub virtiomem_region: Option<Arc<GuestRegionMmap>>,
    pub virtiomem_resize: Option<vm_virtio::Resize>,
    snapshot: Mutex<Option<GuestMemoryLoadGuard<GuestMemoryMmap>>>,
    shared: bool,
    hugepages: bool,
}

#[derive(Debug)]
pub enum Error {
    /// Failed to create shared file.
    SharedFileCreate(io::Error),

    /// Failed to set shared file length.
    SharedFileSetLen(io::Error),

    /// Mmap backed guest memory error
    GuestMemory(MmapError),

    /// Failed to allocate a memory range.
    MemoryRangeAllocation,

    /// Failed to create map region
    MmapRegion(),

    /// Error from region creation
    GuestMemoryRegion(MmapRegionError),

    /// No ACPI slot available
    NoSlotAvailable,

    /// Not enough space in the hotplug RAM region
    InsufficientHotplugRAM,

    /// The requested hotplug memory addition is not a valid size
    InvalidSize,

    /// Failed to set the user memory region.
    SetUserMemoryRegion(kvm_ioctls::Error),

    /// Failed to EventFd.
    EventFdFail(io::Error),

    /// Eventfd write error
    EventfdError(io::Error),

    /// Failed to virtio-mem resize
    VirtioMemResizeFail(vm_virtio::mem::Error),

    /// Cannot restore VM
    Restore(MigratableError),

    /// Cannot create the system allocator
    CreateSystemAllocator,

    /// The number of external backing files doesn't match the number of
    /// memory regions.
    InvalidAmountExternalBackingFiles,
}

const ENABLE_FLAG: usize = 0;
const INSERTING_FLAG: usize = 1;
const REMOVING_FLAG: usize = 2;
const EJECT_FLAG: usize = 3;

const BASE_OFFSET_LOW: u64 = 0;
const BASE_OFFSET_HIGH: u64 = 0x4;
const LENGTH_OFFSET_LOW: u64 = 0x8;
const LENGTH_OFFSET_HIGH: u64 = 0xC;
const STATUS_OFFSET: u64 = 0x14;
const SELECTION_OFFSET: u64 = 0;

// The MMIO address space size is substracted with the size of a 4k page. This
// is done on purpose to workaround a Linux bug when the VMM allocates devices
// at the end of the addressable space.
fn mmio_address_space_size() -> u64 {
    (1 << get_host_cpu_phys_bits()) - 0x1000
}

impl BusDevice for MemoryManager {
    fn read(&mut self, _base: u64, offset: u64, data: &mut [u8]) {
        if self.selected_slot < self.hotplug_slots.len() {
            let state = &self.hotplug_slots[self.selected_slot];
            match offset {
                BASE_OFFSET_LOW => {
                    data.copy_from_slice(&state.base.to_le_bytes()[..4]);
                }
                BASE_OFFSET_HIGH => {
                    data.copy_from_slice(&state.base.to_le_bytes()[4..]);
                }
                LENGTH_OFFSET_LOW => {
                    data.copy_from_slice(&state.length.to_le_bytes()[..4]);
                }
                LENGTH_OFFSET_HIGH => {
                    data.copy_from_slice(&state.length.to_le_bytes()[4..]);
                }
                STATUS_OFFSET => {
                    if state.active {
                        data[0] |= 1 << ENABLE_FLAG;
                    }
                    if state.inserting {
                        data[0] |= 1 << INSERTING_FLAG;
                    }
                    if state.removing {
                        data[0] |= 1 << REMOVING_FLAG;
                    }
                }
                _ => {
                    warn!(
                        "Unexpected offset for accessing memory manager device: {:#}",
                        offset
                    );
                }
            }
        }
    }

    fn write(&mut self, _base: u64, offset: u64, data: &[u8]) {
        match offset {
            SELECTION_OFFSET => {
                self.selected_slot = usize::from(data[0]);
            }
            STATUS_OFFSET => {
                let state = &mut self.hotplug_slots[self.selected_slot];
                // The ACPI code writes back a 1 to acknowledge the insertion
                if (data[0] & (1 << INSERTING_FLAG) == 1 << INSERTING_FLAG) && state.inserting {
                    state.inserting = false;
                }
                // Ditto for removal
                if (data[0] & (1 << REMOVING_FLAG) == 1 << REMOVING_FLAG) && state.removing {
                    state.removing = false;
                }
                // Trigger removal of "DIMM"
                if data[0] & (1 << EJECT_FLAG) == 1 << EJECT_FLAG {
                    warn!("Ejection of memory not currently supported");
                }
            }
            _ => {
                warn!(
                    "Unexpected offset for accessing memory manager device: {:#}",
                    offset
                );
            }
        }
    }
}

impl MemoryManager {
    pub fn new(
        fd: Arc<VmFd>,
        config: &MemoryConfig,
        ext_regions: Option<Vec<MemoryRegion>>,
        prefault: bool,
    ) -> Result<Arc<Mutex<MemoryManager>>, Error> {
        // Init guest memory
        let arch_mem_regions = arch::arch_memory_regions(config.size);

        let ram_regions: Vec<(GuestAddress, usize)> = arch_mem_regions
            .iter()
            .filter(|r| r.2 == RegionType::Ram)
            .map(|r| (r.0, r.1))
            .collect();

        let mut mem_regions = Vec::new();
        if let Some(ext_regions) = &ext_regions {
            if ram_regions.len() > ext_regions.len() {
                return Err(Error::InvalidAmountExternalBackingFiles);
            }

            for region in ext_regions.iter() {
                mem_regions.push(MemoryManager::create_ram_region(
                    &Some(region.backing_file.clone()),
                    region.start_addr,
                    region.size as usize,
                    true,
                    prefault,
                    false,
                    false,
                )?);
            }
        } else {
            for region in ram_regions.iter() {
                mem_regions.push(MemoryManager::create_ram_region(
                    &config.file,
                    region.0,
                    region.1,
                    false,
                    prefault,
                    config.shared,
                    config.hugepages,
                )?);
            }
        }

        let guest_memory =
            GuestMemoryMmap::from_arc_regions(mem_regions).map_err(Error::GuestMemory)?;

        let end_of_device_area = GuestAddress(mmio_address_space_size() - 1);

        let mut start_of_device_area = MemoryManager::start_addr(guest_memory.last_addr(), false);

        let mut virtiomem_region = None;
        let mut virtiomem_resize = None;
        if let Some(size) = config.hotplug_size {
            if config.hotplug_method == HotplugMethod::VirtioMem {
                // Alignment must be "natural" i.e. same as size of block
                let start_addr = GuestAddress(
                    (start_of_device_area.0 + vm_virtio::VIRTIO_MEM_DEFAULT_BLOCK_SIZE - 1)
                        / vm_virtio::VIRTIO_MEM_DEFAULT_BLOCK_SIZE
                        * vm_virtio::VIRTIO_MEM_DEFAULT_BLOCK_SIZE,
                );
                virtiomem_region = Some(MemoryManager::create_ram_region(
                    &config.file,
                    start_addr,
                    size as usize,
                    false,
                    false,
                    config.shared,
                    config.hugepages,
                )?);

                virtiomem_resize = Some(vm_virtio::Resize::new().map_err(Error::EventFdFail)?);

                start_of_device_area = start_addr.unchecked_add(size);
            } else {
                start_of_device_area = start_of_device_area.unchecked_add(size);
            }
        }

        let guest_memory = GuestMemoryAtomic::new(guest_memory);

        let mut hotplug_slots = Vec::with_capacity(HOTPLUG_COUNT);
        hotplug_slots.resize_with(HOTPLUG_COUNT, HotPlugState::default);

        // Both MMIO and PIO address spaces start at address 0.
        let allocator = Arc::new(Mutex::new(
            SystemAllocator::new(
                GuestAddress(0),
                1 << 16 as GuestUsize,
                GuestAddress(0),
                mmio_address_space_size(),
                layout::MEM_32BIT_DEVICES_START,
                layout::MEM_32BIT_DEVICES_SIZE,
                #[cfg(target_arch = "x86_64")]
                vec![GsiApic::new(
                    X86_64_IRQ_BASE,
                    ioapic::NUM_IOAPIC_PINS as u32 - X86_64_IRQ_BASE,
                )],
            )
            .ok_or(Error::CreateSystemAllocator)?,
        ));

        let memory_manager = Arc::new(Mutex::new(MemoryManager {
            guest_memory: guest_memory.clone(),
            next_kvm_memory_slot: 0,
            start_of_device_area,
            end_of_device_area,
            fd,
            hotplug_slots,
            selected_slot: 0,
            backing_file: config.file.clone(),
            mergeable: config.mergeable,
            allocator: allocator.clone(),
            hotplug_method: config.hotplug_method.clone(),
            boot_ram: config.size,
            current_ram: config.size,
            next_hotplug_slot: 0,
            virtiomem_region: virtiomem_region.clone(),
            virtiomem_resize,
            snapshot: Mutex::new(None),
            shared: config.shared,
            hugepages: config.hugepages,
        }));

        guest_memory.memory().with_regions(|_, region| {
            let _ = memory_manager.lock().unwrap().create_userspace_mapping(
                region.start_addr().raw_value(),
                region.len() as u64,
                region.as_ptr() as u64,
                config.mergeable,
                false,
            )?;
            Ok(())
        })?;

        if let Some(region) = virtiomem_region {
            memory_manager.lock().unwrap().create_userspace_mapping(
                region.start_addr().raw_value(),
                region.len() as u64,
                region.as_ptr() as u64,
                config.mergeable,
                false,
            )?;
            allocator
                .lock()
                .unwrap()
                .allocate_mmio_addresses(Some(region.start_addr()), region.len(), None)
                .ok_or(Error::MemoryRangeAllocation)?;
        }

        // Allocate RAM and Reserved address ranges.
        for region in arch_mem_regions.iter() {
            allocator
                .lock()
                .unwrap()
                .allocate_mmio_addresses(Some(region.0), region.1 as GuestUsize, None)
                .ok_or(Error::MemoryRangeAllocation)?;
        }

        Ok(memory_manager)
    }

    pub fn new_from_snapshot(
        snapshot: &Snapshot,
        fd: Arc<VmFd>,
        config: &MemoryConfig,
        source_url: &str,
        prefault: bool,
    ) -> Result<Arc<Mutex<MemoryManager>>, Error> {
        let url = Url::parse(source_url).unwrap();
        /* url must be valid dir which is verified in recv_vm_snapshot() */
        let vm_snapshot_path = url.to_file_path().unwrap();

        if let Some(mem_section) = snapshot
            .snapshot_data
            .get(&format!("{}-section", MEMORY_MANAGER_SNAPSHOT_ID))
        {
            let mem_snapshot: MemoryManagerSnapshotData =
                match serde_json::from_slice(&mem_section.snapshot) {
                    Ok(snapshot) => snapshot,
                    Err(error) => {
                        return Err(Error::Restore(MigratableError::Restore(anyhow!(
                            "Could not deserialize MemoryManager {}",
                            error
                        ))))
                    }
                };

            let mut ext_regions = mem_snapshot.memory_regions;
            for region in ext_regions.iter_mut() {
                let mut memory_region_path = vm_snapshot_path.clone();
                memory_region_path.push(region.backing_file.clone());
                region.backing_file = memory_region_path;
            }

            // In case there was no backing file, we can safely use CoW by
            // mapping the source files provided for restoring. This case
            // allows for a faster VM restoration and does not require us to
            // fill the memory content, hence we can return right away.
            if config.file.is_none() {
                return MemoryManager::new(fd, config, Some(ext_regions), prefault);
            };

            let memory_manager = MemoryManager::new(fd, config, None, false)?;
            let guest_memory = memory_manager.lock().unwrap().guest_memory();

            // In case the previous config was using a backing file, this means
            // it was MAP_SHARED, therefore we must copy the content into the
            // new regions so that we can still use MAP_SHARED when restoring
            // the VM.
            guest_memory.memory().with_regions(|index, region| {
                // Open (read only) the snapshot file for the given region.
                let mut memory_region_file = OpenOptions::new()
                    .read(true)
                    .open(&ext_regions[index].backing_file)
                    .map_err(|e| Error::Restore(MigratableError::MigrateReceive(e.into())))?;

                // Fill the region with the file content.
                region
                    .read_from(
                        MemoryRegionAddress(0),
                        &mut memory_region_file,
                        region.len().try_into().unwrap(),
                    )
                    .map_err(|e| Error::Restore(MigratableError::MigrateReceive(e.into())))?;

                Ok(())
            })?;

            Ok(memory_manager)
        } else {
            Err(Error::Restore(MigratableError::Restore(anyhow!(
                "Could not find {}-section from snapshot",
                MEMORY_MANAGER_SNAPSHOT_ID
            ))))
        }
    }

    fn memfd_create(name: &ffi::CStr, flags: u32) -> Result<RawFd, io::Error> {
        let res = unsafe { libc::syscall(libc::SYS_memfd_create, name.as_ptr(), flags) };

        if res < 0 {
            Err(io::Error::last_os_error())
        } else {
            Ok(res as RawFd)
        }
    }

    fn create_ram_region(
        backing_file: &Option<PathBuf>,
        start_addr: GuestAddress,
        size: usize,
        copy_on_write: bool,
        prefault: bool,
        shared: bool,
        hugepages: bool,
    ) -> Result<Arc<GuestRegionMmap>, Error> {
        Ok(Arc::new(match backing_file {
            Some(ref file) => {
                let f = if file.is_dir() {
                    let fs_str = format!("{}{}", file.display(), "/tmpfile_XXXXXX");
                    let fs = ffi::CString::new(fs_str).unwrap();
                    let mut path = fs.as_bytes_with_nul().to_owned();
                    let path_ptr = path.as_mut_ptr() as *mut _;
                    let fd = unsafe { libc::mkstemp(path_ptr) };
                    unsafe { libc::unlink(path_ptr) };
                    unsafe { File::from_raw_fd(fd) }
                } else {
                    OpenOptions::new()
                        .read(true)
                        .write(true)
                        .open(file)
                        .map_err(Error::SharedFileCreate)?
                };

                f.set_len(size as u64).map_err(Error::SharedFileSetLen)?;

                let mut mmap_flags = if copy_on_write {
                    libc::MAP_NORESERVE | libc::MAP_PRIVATE
                } else {
                    libc::MAP_NORESERVE | libc::MAP_SHARED
                };
                if prefault {
                    mmap_flags |= libc::MAP_POPULATE;
                }
                GuestRegionMmap::new(
                    MmapRegion::build(
                        Some(FileOffset::new(f, 0)),
                        size,
                        libc::PROT_READ | libc::PROT_WRITE,
                        mmap_flags,
                    )
                    .map_err(Error::GuestMemoryRegion)?,
                    start_addr,
                )
                .map_err(Error::GuestMemory)?
            }
            None => {
                let fd = Self::memfd_create(
                    &ffi::CString::new("ch_ram").unwrap(),
                    if hugepages {
                        libc::MFD_HUGETLB | libc::MAP_HUGE_2MB as u32
                    } else {
                        0
                    },
                )
                .map_err(Error::SharedFileCreate)?;

                let f = unsafe { File::from_raw_fd(fd) };
                f.set_len(size as u64).map_err(Error::SharedFileSetLen)?;

                let mmap_flags = libc::MAP_NORESERVE
                    | if shared {
                        libc::MAP_SHARED
                    } else {
                        libc::MAP_PRIVATE
                    };
                GuestRegionMmap::new(
                    MmapRegion::build(
                        Some(FileOffset::new(f, 0)),
                        size,
                        libc::PROT_READ | libc::PROT_WRITE,
                        mmap_flags,
                    )
                    .map_err(Error::GuestMemoryRegion)?,
                    start_addr,
                )
                .map_err(Error::GuestMemory)?
            }
        }))
    }

    // Update the GuestMemoryMmap with the new range
    fn add_region(&mut self, region: Arc<GuestRegionMmap>) -> Result<(), Error> {
        let guest_memory = self
            .guest_memory
            .memory()
            .insert_region(region)
            .map_err(Error::GuestMemory)?;
        self.guest_memory.lock().unwrap().replace(guest_memory);

        Ok(())
    }

    //
    // Calculate the start address of an area next to RAM.
    //
    // If the next area is device space, there is no gap.
    // If the next area is hotplugged RAM, the start address needs to be aligned
    // to 128MiB boundary, and a gap of 256MiB need to be set before it.
    // On x86_64, it must also start at the 64bit start.
    fn start_addr(mem_end: GuestAddress, with_gap: bool) -> GuestAddress {
        let start_addr = if with_gap {
            GuestAddress((mem_end.0 + 1 + (256 << 20)) & !((128 << 20) - 1))
        } else {
            mem_end.unchecked_add(1)
        };

        #[cfg(target_arch = "x86_64")]
        let start_addr = if mem_end < arch::layout::MEM_32BIT_RESERVED_START {
            arch::layout::RAM_64BIT_START
        } else {
            start_addr
        };

        start_addr
    }

    fn hotplug_ram_region(&mut self, size: usize) -> Result<Arc<GuestRegionMmap>, Error> {
        info!("Hotplugging new RAM: {}", size);

        // Check that there is a free slot
        if self.next_hotplug_slot >= HOTPLUG_COUNT {
            return Err(Error::NoSlotAvailable);
        }

        // "Inserted" DIMM must have a size that is a multiple of 128MiB
        if size % (128 << 20) != 0 {
            return Err(Error::InvalidSize);
        }

        let start_addr = MemoryManager::start_addr(self.guest_memory.memory().last_addr(), true);

        if start_addr.checked_add(size.try_into().unwrap()).unwrap() >= self.start_of_device_area()
        {
            return Err(Error::InsufficientHotplugRAM);
        }

        // Allocate memory for the region
        let region = MemoryManager::create_ram_region(
            &self.backing_file,
            start_addr,
            size,
            false,
            false,
            self.shared,
            self.hugepages,
        )?;

        // Map it into the guest
        self.create_userspace_mapping(
            region.start_addr().0,
            region.len() as u64,
            region.as_ptr() as u64,
            self.mergeable,
            false,
        )?;

        // Tell the allocator
        self.allocator
            .lock()
            .unwrap()
            .allocate_mmio_addresses(Some(start_addr), size as GuestUsize, None)
            .ok_or(Error::MemoryRangeAllocation)?;

        // Update the slot so that it can be queried via the I/O port
        let mut slot = &mut self.hotplug_slots[self.next_hotplug_slot];
        slot.active = true;
        slot.inserting = true;
        slot.base = region.start_addr().0;
        slot.length = region.len() as u64;

        self.next_hotplug_slot += 1;

        self.add_region(Arc::clone(&region))?;

        Ok(region)
    }

    pub fn guest_memory(&self) -> GuestMemoryAtomic<GuestMemoryMmap> {
        self.guest_memory.clone()
    }

    pub fn allocator(&self) -> Arc<Mutex<SystemAllocator>> {
        self.allocator.clone()
    }

    pub fn start_of_device_area(&self) -> GuestAddress {
        self.start_of_device_area
    }

    pub fn end_of_device_area(&self) -> GuestAddress {
        self.end_of_device_area
    }

    pub fn allocate_kvm_memory_slot(&mut self) -> u32 {
        let slot_id = self.next_kvm_memory_slot;
        self.next_kvm_memory_slot += 1;
        slot_id
    }

    pub fn create_userspace_mapping(
        &mut self,
        guest_phys_addr: u64,
        memory_size: u64,
        userspace_addr: u64,
        mergeable: bool,
        readonly: bool,
    ) -> Result<u32, Error> {
        let slot = self.allocate_kvm_memory_slot();
        let mem_region = kvm_userspace_memory_region {
            slot,
            guest_phys_addr,
            memory_size,
            userspace_addr,
            flags: if readonly { KVM_MEM_READONLY } else { 0 },
        };

        // Safe because the guest regions are guaranteed not to overlap.
        unsafe { self.fd.set_user_memory_region(mem_region) }
            .map_err(Error::SetUserMemoryRegion)?;

        // Mark the pages as mergeable if explicitly asked for.
        if mergeable {
            // Safe because the address and size are valid since the
            // mmap succeeded.
            let ret = unsafe {
                libc::madvise(
                    userspace_addr as *mut libc::c_void,
                    memory_size as libc::size_t,
                    libc::MADV_MERGEABLE,
                )
            };
            if ret != 0 {
                let err = io::Error::last_os_error();
                // Safe to unwrap because the error is constructed with
                // last_os_error(), which ensures the output will be Some().
                let errno = err.raw_os_error().unwrap();
                if errno == libc::EINVAL {
                    warn!("kernel not configured with CONFIG_KSM");
                } else {
                    warn!("madvise error: {}", err);
                }
                warn!("failed to mark pages as mergeable");
            }
        }

        info!(
            "Created userspace mapping: {:x} -> {:x} {:x}",
            guest_phys_addr, userspace_addr, memory_size
        );

        Ok(slot)
    }

    pub fn remove_userspace_mapping(
        &mut self,
        guest_phys_addr: u64,
        memory_size: u64,
        userspace_addr: u64,
        mergeable: bool,
        slot: u32,
    ) -> Result<(), Error> {
        let mem_region = kvm_userspace_memory_region {
            slot,
            guest_phys_addr,
            memory_size: 0,
            userspace_addr,
            flags: 0,
        };

        // Safe to remove because we know the region exist.
        unsafe { self.fd.set_user_memory_region(mem_region) }
            .map_err(Error::SetUserMemoryRegion)?;

        // Mark the pages as unmergeable if there were previously marked as
        // mergeable.
        if mergeable {
            // Safe because the address and size are valid as the region was
            // previously advised.
            let ret = unsafe {
                libc::madvise(
                    userspace_addr as *mut libc::c_void,
                    memory_size as libc::size_t,
                    libc::MADV_UNMERGEABLE,
                )
            };
            if ret != 0 {
                let err = io::Error::last_os_error();
                // Safe to unwrap because the error is constructed with
                // last_os_error(), which ensures the output will be Some().
                let errno = err.raw_os_error().unwrap();
                if errno == libc::EINVAL {
                    warn!("kernel not configured with CONFIG_KSM");
                } else {
                    warn!("madvise error: {}", err);
                }
                warn!("failed to mark pages as unmergeable");
            }
        }

        info!(
            "Removed userspace mapping: {:x} -> {:x} {:x}",
            guest_phys_addr, userspace_addr, memory_size
        );

        Ok(())
    }

    pub fn virtiomem_resize(&mut self, size: u64) -> Result<(), Error> {
        let region = self.virtiomem_region.take();
        if let Some(region) = region {
            self.add_region(region)?;
        }

        if let Some(resize) = &self.virtiomem_resize {
            resize.work(size).map_err(Error::VirtioMemResizeFail)?;
        } else {
            panic!("should not fail here");
        }

        Ok(())
    }

    /// In case this function resulted in adding a new memory region to the
    /// guest memory, the new region is returned to the caller. The virtio-mem
    /// use case never adds a new region as the whole hotpluggable memory has
    /// already been allocated at boot time.
    pub fn resize(&mut self, desired_ram: u64) -> Result<Option<Arc<GuestRegionMmap>>, Error> {
        let mut region: Option<Arc<GuestRegionMmap>> = None;
        match self.hotplug_method {
            HotplugMethod::VirtioMem => {
                if desired_ram >= self.boot_ram {
                    self.virtiomem_resize(desired_ram - self.boot_ram)?;
                    self.current_ram = desired_ram;
                }
            }
            HotplugMethod::Acpi => {
                if desired_ram >= self.current_ram {
                    region =
                        Some(self.hotplug_ram_region((desired_ram - self.current_ram) as usize)?);
                    self.current_ram = desired_ram;
                }
            }
        }
        Ok(region)
    }
}

#[cfg(feature = "acpi")]
struct MemoryNotify {
    slot_id: usize,
}

#[cfg(feature = "acpi")]
impl Aml for MemoryNotify {
    fn to_aml_bytes(&self) -> Vec<u8> {
        let object = aml::Path::new(&format!("M{:03}", self.slot_id));
        aml::If::new(
            &aml::Equal::new(&aml::Arg(0), &self.slot_id),
            vec![&aml::Notify::new(&object, &aml::Arg(1))],
        )
        .to_aml_bytes()
    }
}

#[cfg(feature = "acpi")]
struct MemorySlot {
    slot_id: usize,
}

#[cfg(feature = "acpi")]
impl Aml for MemorySlot {
    fn to_aml_bytes(&self) -> Vec<u8> {
        aml::Device::new(
            format!("M{:03}", self.slot_id).as_str().into(),
            vec![
                &aml::Name::new("_HID".into(), &aml::EISAName::new("PNP0C80")),
                &aml::Name::new("_UID".into(), &self.slot_id),
                /*
                _STA return value:
                Bit [0] – Set if the device is present.
                Bit [1] – Set if the device is enabled and decoding its resources.
                Bit [2] – Set if the device should be shown in the UI.
                Bit [3] – Set if the device is functioning properly (cleared if device failed its diagnostics).
                Bit [4] – Set if the battery is present.
                Bits [31:5] – Reserved (must be cleared).
                */
                &aml::Method::new(
                    "_STA".into(),
                    0,
                    false,
                    // Call into MSTA method which will interrogate device
                    vec![&aml::Return::new(&aml::MethodCall::new(
                        "MSTA".into(),
                        vec![&self.slot_id],
                    ))],
                ),
                // Get details of memory
                &aml::Method::new(
                    "_CRS".into(),
                    0,
                    false,
                    // Call into MCRS which provides actual memory details
                    vec![&aml::Return::new(&aml::MethodCall::new(
                        "MCRS".into(),
                        vec![&self.slot_id],
                    ))],
                ),
                // We don't expose any NUMA characteristics so all memory is in the same "proximity domain"
                &aml::Method::new(
                    "_PXM".into(),
                    0,
                    false,
                    // We aren't NUMA so associate all RAM into the same proximity region (zero)
                    vec![&aml::Return::new(&0u32)],
                ),
            ],
        )
        .to_aml_bytes()
    }
}

#[cfg(feature = "acpi")]
struct MemorySlots {
    slots: usize,
}

#[cfg(feature = "acpi")]
impl Aml for MemorySlots {
    fn to_aml_bytes(&self) -> Vec<u8> {
        let mut bytes = Vec::new();

        for slot_id in 0..self.slots {
            bytes.extend_from_slice(&MemorySlot { slot_id }.to_aml_bytes());
        }

        bytes
    }
}

#[cfg(feature = "acpi")]
struct MemoryMethods {
    slots: usize,
}

#[cfg(feature = "acpi")]
impl Aml for MemoryMethods {
    fn to_aml_bytes(&self) -> Vec<u8> {
        let mut bytes = Vec::new();
        // Add "MTFY" notification method
        let mut memory_notifies = Vec::new();
        for slot_id in 0..self.slots {
            memory_notifies.push(MemoryNotify { slot_id });
        }

        let mut memory_notifies_refs: Vec<&dyn aml::Aml> = Vec::new();
        for memory_notifier in memory_notifies.iter() {
            memory_notifies_refs.push(memory_notifier);
        }

        bytes.extend_from_slice(
            &aml::Method::new("MTFY".into(), 2, true, memory_notifies_refs).to_aml_bytes(),
        );

        // MSCN method
        bytes.extend_from_slice(
            &aml::Method::new(
                "MSCN".into(),
                0,
                true,
                vec![
                    // Take lock defined above
                    &aml::Acquire::new("MLCK".into(), 0xfff),
                    &aml::Store::new(&aml::Local(0), &aml::ZERO),
                    &aml::While::new(
                        &aml::LessThan::new(&aml::Local(0), &self.slots),
                        vec![
                            // Write slot number (in first argument) to I/O port via field
                            &aml::Store::new(&aml::Path::new("\\_SB_.MHPC.MSEL"), &aml::Local(0)),
                            // Check if MINS bit is set (inserting)
                            &aml::If::new(
                                &aml::Equal::new(&aml::Path::new("\\_SB_.MHPC.MINS"), &aml::ONE),
                                // Notify device if it is
                                vec![
                                    &aml::MethodCall::new(
                                        "MTFY".into(),
                                        vec![&aml::Local(0), &aml::ONE],
                                    ),
                                    // Reset MINS bit
                                    &aml::Store::new(
                                        &aml::Path::new("\\_SB_.MHPC.MINS"),
                                        &aml::ONE,
                                    ),
                                ],
                            ),
                            // Check if MRMV bit is set
                            &aml::If::new(
                                &aml::Equal::new(&aml::Path::new("\\_SB_.MHPC.MRMV"), &aml::ONE),
                                // Notify device if it is (with the eject constant 0x3)
                                vec![
                                    &aml::MethodCall::new(
                                        "MTFY".into(),
                                        vec![&aml::Local(0), &3u8],
                                    ),
                                    // Reset MRMV bit
                                    &aml::Store::new(
                                        &aml::Path::new("\\_SB_.MHPC.MRMV"),
                                        &aml::ONE,
                                    ),
                                ],
                            ),
                            &aml::Add::new(&aml::Local(0), &aml::Local(0), &aml::ONE),
                        ],
                    ),
                    // Release lock
                    &aml::Release::new("MLCK".into()),
                ],
            )
            .to_aml_bytes(),
        );

        bytes.extend_from_slice(
            // Memory status method
            &aml::Method::new(
                "MSTA".into(),
                1,
                true,
                vec![
                    // Take lock defined above
                    &aml::Acquire::new("MLCK".into(), 0xfff),
                    // Write slot number (in first argument) to I/O port via field
                    &aml::Store::new(&aml::Path::new("\\_SB_.MHPC.MSEL"), &aml::Arg(0)),
                    &aml::Store::new(&aml::Local(0), &aml::ZERO),
                    // Check if MEN_ bit is set, if so make the local variable 0xf (see _STA for details of meaning)
                    &aml::If::new(
                        &aml::Equal::new(&aml::Path::new("\\_SB_.MHPC.MEN_"), &aml::ONE),
                        vec![&aml::Store::new(&aml::Local(0), &0xfu8)],
                    ),
                    // Release lock
                    &aml::Release::new("MLCK".into()),
                    // Return 0 or 0xf
                    &aml::Return::new(&aml::Local(0)),
                ],
            )
            .to_aml_bytes(),
        );

        bytes.extend_from_slice(
            // Memory range method
            &aml::Method::new(
                "MCRS".into(),
                1,
                true,
                vec![
                    // Take lock defined above
                    &aml::Acquire::new("MLCK".into(), 0xfff),
                    // Write slot number (in first argument) to I/O port via field
                    &aml::Store::new(&aml::Path::new("\\_SB_.MHPC.MSEL"), &aml::Arg(0)),
                    &aml::Name::new(
                        "MR64".into(),
                        &aml::ResourceTemplate::new(vec![&aml::AddressSpace::new_memory(
                            aml::AddressSpaceCachable::Cacheable,
                            true,
                            0x0000_0000_0000_0000u64,
                            0xFFFF_FFFF_FFFF_FFFEu64,
                        )]),
                    ),
                    &aml::CreateField::<u32>::new(&aml::Path::new("MR64"), &14usize, "MINL".into()),
                    &aml::CreateField::<u32>::new(&aml::Path::new("MR64"), &18usize, "MINH".into()),
                    &aml::CreateField::<u32>::new(&aml::Path::new("MR64"), &22usize, "MAXL".into()),
                    &aml::CreateField::<u32>::new(&aml::Path::new("MR64"), &26usize, "MAXH".into()),
                    &aml::CreateField::<u32>::new(&aml::Path::new("MR64"), &38usize, "LENL".into()),
                    &aml::CreateField::<u32>::new(&aml::Path::new("MR64"), &42usize, "LENH".into()),
                    &aml::Store::new(&aml::Path::new("MINL"), &aml::Path::new("\\_SB_.MHPC.MHBL")),
                    &aml::Store::new(&aml::Path::new("MINH"), &aml::Path::new("\\_SB_.MHPC.MHBH")),
                    &aml::Store::new(&aml::Path::new("LENL"), &aml::Path::new("\\_SB_.MHPC.MHLL")),
                    &aml::Store::new(&aml::Path::new("LENH"), &aml::Path::new("\\_SB_.MHPC.MHLH")),
                    &aml::Add::new(
                        &aml::Path::new("MAXL"),
                        &aml::Path::new("MINL"),
                        &aml::Path::new("LENL"),
                    ),
                    &aml::Add::new(
                        &aml::Path::new("MAXH"),
                        &aml::Path::new("MINH"),
                        &aml::Path::new("LENH"),
                    ),
                    &aml::Subtract::new(
                        &aml::Path::new("MAXH"),
                        &aml::Path::new("MAXH"),
                        &aml::ONE,
                    ),
                    // Release lock
                    &aml::Release::new("MLCK".into()),
                    &aml::Return::new(&aml::Path::new("MR64")),
                ],
            )
            .to_aml_bytes(),
        );
        bytes
    }
}

#[cfg(feature = "acpi")]
impl Aml for MemoryManager {
    fn to_aml_bytes(&self) -> Vec<u8> {
        let mut bytes = Vec::new();

        // Memory Hotplug Controller
        bytes.extend_from_slice(
            &aml::Device::new(
                "_SB_.MHPC".into(),
                vec![
                    &aml::Name::new("_HID".into(), &aml::EISAName::new("PNP0A06")),
                    // Mutex to protect concurrent access as we write to choose slot and then read back status
                    &aml::Mutex::new("MLCK".into(), 0),
                    // I/O port for memory controller
                    &aml::Name::new(
                        "_CRS".into(),
                        &aml::ResourceTemplate::new(vec![&aml::IO::new(
                            0x0a00, 0x0a00, 0x01, 0x18,
                        )]),
                    ),
                    // OpRegion and Fields map I/O port into individual field values
                    &aml::OpRegion::new("MHPR".into(), aml::OpRegionSpace::SystemIO, 0xa00, 0x18),
                    &aml::Field::new(
                        "MHPR".into(),
                        aml::FieldAccessType::DWord,
                        aml::FieldUpdateRule::Preserve,
                        vec![
                            aml::FieldEntry::Named(*b"MHBL", 32), // Base (low 4 bytes)
                            aml::FieldEntry::Named(*b"MHBH", 32), // Base (high 4 bytes)
                            aml::FieldEntry::Named(*b"MHLL", 32), // Length (low 4 bytes)
                            aml::FieldEntry::Named(*b"MHLH", 32), // Length (high 4 bytes)
                        ],
                    ),
                    &aml::Field::new(
                        "MHPR".into(),
                        aml::FieldAccessType::DWord,
                        aml::FieldUpdateRule::Preserve,
                        vec![
                            aml::FieldEntry::Reserved(128),
                            aml::FieldEntry::Named(*b"MHPX", 32), // PXM
                        ],
                    ),
                    &aml::Field::new(
                        "MHPR".into(),
                        aml::FieldAccessType::Byte,
                        aml::FieldUpdateRule::WriteAsZeroes,
                        vec![
                            aml::FieldEntry::Reserved(160),
                            aml::FieldEntry::Named(*b"MEN_", 1), // Enabled
                            aml::FieldEntry::Named(*b"MINS", 1), // Inserting
                            aml::FieldEntry::Named(*b"MRMV", 1), // Removing
                            aml::FieldEntry::Named(*b"MEJ0", 1), // Ejecting
                        ],
                    ),
                    &aml::Field::new(
                        "MHPR".into(),
                        aml::FieldAccessType::DWord,
                        aml::FieldUpdateRule::Preserve,
                        vec![
                            aml::FieldEntry::Named(*b"MSEL", 32), // Selector
                            aml::FieldEntry::Named(*b"MOEV", 32), // Event
                            aml::FieldEntry::Named(*b"MOSC", 32), // OSC
                        ],
                    ),
                    &MemoryMethods {
                        slots: self.hotplug_slots.len(),
                    },
                    &MemorySlots {
                        slots: self.hotplug_slots.len(),
                    },
                ],
            )
            .to_aml_bytes(),
        );

        bytes
    }
}

impl Pausable for MemoryManager {}

#[derive(Serialize, Deserialize)]
#[serde(remote = "GuestAddress")]
pub struct GuestAddressDef(pub u64);

#[derive(Serialize, Deserialize)]
pub struct MemoryRegion {
    backing_file: PathBuf,
    #[serde(with = "GuestAddressDef")]
    start_addr: GuestAddress,
    size: GuestUsize,
}

#[derive(Serialize, Deserialize)]
pub struct MemoryManagerSnapshotData {
    memory_regions: Vec<MemoryRegion>,
}

impl Snapshottable for MemoryManager {
    fn id(&self) -> String {
        MEMORY_MANAGER_SNAPSHOT_ID.to_string()
    }

    fn snapshot(&self) -> result::Result<Snapshot, MigratableError> {
        let mut memory_manager_snapshot = Snapshot::new(MEMORY_MANAGER_SNAPSHOT_ID);
        let guest_memory = self.guest_memory.memory();

        let mut memory_regions: Vec<MemoryRegion> = Vec::with_capacity(10);

        guest_memory.with_regions_mut(|index, region| {
            if region.len() == 0 {
                return Err(MigratableError::Snapshot(anyhow!("Zero length region")));
            }

            memory_regions.push(MemoryRegion {
                backing_file: PathBuf::from(format!("memory-region-{}", index)),
                start_addr: region.start_addr(),
                size: region.len(),
            });

            Ok(())
        })?;

        let snapshot_data_section =
            serde_json::to_vec(&MemoryManagerSnapshotData { memory_regions })
                .map_err(|e| MigratableError::Snapshot(e.into()))?;

        memory_manager_snapshot.add_data_section(SnapshotDataSection {
            id: format!("{}-section", MEMORY_MANAGER_SNAPSHOT_ID),
            snapshot: snapshot_data_section,
        });

        let mut memory_snapshot = self.snapshot.lock().unwrap();
        *memory_snapshot = Some(guest_memory);

        Ok(memory_manager_snapshot)
    }
}

impl Transportable for MemoryManager {
    fn send(
        &self,
        _snapshot: &Snapshot,
        destination_url: &str,
    ) -> result::Result<(), MigratableError> {
        let url = Url::parse(destination_url).map_err(|e| {
            MigratableError::MigrateSend(anyhow!("Could not parse destination URL: {}", e))
        })?;

        match url.scheme() {
            "file" => {
                let vm_memory_snapshot_path = url
                    .to_file_path()
                    .map_err(|_| {
                        MigratableError::MigrateSend(anyhow!(
                            "Could not convert file URL to a file path"
                        ))
                    })
                    .and_then(|path| {
                        if !path.is_dir() {
                            return Err(MigratableError::MigrateSend(anyhow!(
                                "Destination is not a directory"
                            )));
                        }
                        Ok(path)
                    })?;

                if let Some(guest_memory) = &*self.snapshot.lock().unwrap() {
                    guest_memory.with_regions_mut(|index, region| {
                        let mut memory_region_path = vm_memory_snapshot_path.clone();
                        memory_region_path.push(format!("memory-region-{}", index));

                        // Create the snapshot file for the region
                        let mut memory_region_file = OpenOptions::new()
                            .read(true)
                            .write(true)
                            .create_new(true)
                            .open(memory_region_path)
                            .map_err(|e| MigratableError::MigrateSend(e.into()))?;

                        guest_memory
                            .write_to(
                                region.start_addr(),
                                &mut memory_region_file,
                                region.len().try_into().unwrap(),
                            )
                            .map_err(|e| MigratableError::MigrateSend(e.into()))?;

                        Ok(())
                    })?;
                }
            }
            _ => {
                return Err(MigratableError::MigrateSend(anyhow!(
                    "Unsupported VM transport URL scheme: {}",
                    url.scheme()
                )))
            }
        }
        Ok(())
    }
}
impl Migratable for MemoryManager {}