Makes RAM belong to hypervisor (#976)

src/core.h

@@ -170,42 +170,6 @@ struct Vmm *vmm_run(const char *kernel,
 
 struct RustError *vmm_draw(struct Vmm *vmm);
 
-#if defined(__linux__)
-extern int kvm_check_version(int kvm, bool *compat);
-#endif
-
-#if defined(__linux__)
-extern int kvm_max_vcpus(int kvm, size_t *max);
-#endif
-
-#if defined(__linux__)
-extern int kvm_create_vm(int kvm, int *fd);
-#endif
-
-#if defined(__linux__)
-extern int kvm_get_vcpu_mmap_size(int kvm);
-#endif
-
-#if defined(__linux__)
-extern int kvm_set_user_memory_region(int vm,
-                                      uint32_t slot,
-                                      uint64_t addr,
-                                      uint64_t len,
-                                      void *mem);
-#endif
-
-#if defined(__linux__)
-extern int kvm_create_vcpu(int vm, uint32_t id, int *fd);
-#endif
-
-#if defined(__linux__)
-extern int kvm_run(int vcpu);
-#endif
-
-#if defined(__linux__)
-extern int kvm_translate(int vcpu, kvm_translation *arg);
-#endif
-
 #ifdef __cplusplus
 } // extern "C"
 #endif // __cplusplus

src/core/src/vmm/aarch64.rs

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 use super::hv::{Cpu, CpuFeats, CpuStates, Pstate};
-use super::hw::RamMap;
+use super::ram::RamMap;
 use super::MainCpuError;
 
 pub fn setup_main_cpu(

src/core/src/vmm/hv/linux/mod.rs

@@ -5,7 +5,7 @@ use self::ffi::{
     kvm_set_user_memory_region,
 };
 use super::{CpuFeats, Hypervisor};
-use crate::vmm::hw::Ram;
+use crate::vmm::ram::Ram;
 use crate::vmm::VmmError;
 use libc::{mmap, open, MAP_FAILED, MAP_PRIVATE, O_RDWR, PROT_READ, PROT_WRITE};
 use std::os::fd::{AsRawFd, FromRawFd, OwnedFd};
@@ -20,20 +20,7 @@ mod ffi;
 mod regs;
 mod run;
 
-/// Implementation of [`Hypervisor`] using KVM.
-///
-/// Fields in this struct need to drop in a correct order (e.g. vm must be dropped before ram).
-pub struct Kvm {
-    vcpu_mmap_size: usize,
-    vm: OwnedFd,
-    #[allow(dead_code)] // ram are needed by vm.
-    ram: Arc<Ram>,
-    #[allow(dead_code)] // kvm are needed by vm.
-    kvm: OwnedFd,
-}
-
-impl Kvm {
-    pub fn new(cpu: usize, ram: Arc<Ram>) -> Result<Self, VmmError> {
+pub fn new(cpu: usize, ram: Ram) -> Result<impl Hypervisor, VmmError> {
     use std::io::Error;
 
     // Open KVM device.
@@ -94,13 +81,23 @@ impl Kvm {
         v => return Err(VmmError::MapRamFailed(Error::from_raw_os_error(v))),
     }
 
-        Ok(Self {
+    Ok(Kvm {
         vcpu_mmap_size,
         vm,
         ram,
         kvm,
     })
 }
+
+/// Implementation of [`Hypervisor`] using KVM.
+///
+/// Fields in this struct need to drop in a correct order (e.g. vm must be dropped before ram).
+struct Kvm {
+    vcpu_mmap_size: usize,
+    vm: OwnedFd,
+    ram: Ram,
+    #[allow(dead_code)] // kvm are needed by vm.
+    kvm: OwnedFd,
 }
 
 impl Hypervisor for Kvm {
@@ -111,6 +108,14 @@ impl Hypervisor for Kvm {
         Ok(CpuFeats {})
     }
 
+    fn ram(&self) -> &Ram {
+        &self.ram
+    }
+
+    fn ram_mut(&mut self) -> &mut Ram {
+        &mut self.ram
+    }
+
     fn create_cpu(&self, id: usize) -> Result<Self::Cpu<'_>, Self::CpuErr> {
         use std::io::Error;
 

src/core/src/vmm/hv/macos/mod.rs

@@ -2,12 +2,11 @@
 use self::cpu::HfCpu;
 use self::vm::Vm;
 use super::{CpuFeats, Hypervisor};
-use crate::vmm::hw::Ram;
+use crate::vmm::ram::Ram;
 use crate::vmm::VmmError;
 use hv_sys::hv_vcpu_create;
 use std::ffi::c_int;
 use std::num::NonZero;
-use std::sync::Arc;
 use thiserror::Error;
 
 #[cfg_attr(target_arch = "aarch64", path = "aarch64.rs")]
@@ -16,16 +15,7 @@ mod arch;
 mod cpu;
 mod vm;
 
-/// Implementation of [`Hypervisor`] using Hypervisor Framework.
-///
-/// Fields in this struct need to drop in a correct order.
-pub struct Hf {
-    vm: Vm,
-    ram: Arc<Ram>,
-}
-
-impl Hf {
-    pub fn new(_: usize, ram: Arc<Ram>) -> Result<Self, VmmError> {
+pub fn new(_: usize, ram: Ram) -> Result<impl Hypervisor, VmmError> {
     // Create a VM.
     let vm = Vm::new().map_err(VmmError::CreateVmFailed)?;
 
@@ -33,8 +23,15 @@ impl Hf {
     vm.vm_map(ram.host_addr().cast_mut().cast(), 0, ram.len())
         .map_err(VmmError::MapRamFailed)?;
 
-        Ok(Self { vm, ram })
+    Ok(Hf { vm, ram })
 }
+
+/// Implementation of [`Hypervisor`] using Hypervisor Framework.
+///
+/// Fields in this struct need to drop in a correct order.
+struct Hf {
+    vm: Vm,
+    ram: Ram,
 }
 
 impl Hypervisor for Hf {
@@ -120,6 +117,14 @@ impl Hypervisor for Hf {
         Ok(CpuFeats {})
     }
 
+    fn ram(&self) -> &Ram {
+        &self.ram
+    }
+
+    fn ram_mut(&mut self) -> &mut Ram {
+        &mut self.ram
+    }
+
     fn create_cpu(&self, _: usize) -> Result<Self::Cpu<'_>, Self::CpuErr> {
         let mut instance = 0;
 

src/core/src/vmm/hv/mod.rs

@@ -1,35 +1,17 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
-use super::hw::Ram;
-use super::VmmError;
+use super::ram::Ram;
 use std::error::Error;
-use std::sync::Arc;
 
 pub use self::arch::*;
+pub use self::os::new;
 
 #[cfg_attr(target_arch = "aarch64", path = "aarch64.rs")]
 #[cfg_attr(target_arch = "x86_64", path = "x86_64.rs")]
 mod arch;
-#[cfg(target_os = "linux")]
-mod linux;
-#[cfg(target_os = "macos")]
-mod macos;
-#[cfg(target_os = "windows")]
-mod windows;
-
-#[cfg(target_os = "linux")]
-pub fn new(cpu: usize, ram: Arc<Ram>) -> Result<impl Hypervisor, VmmError> {
-    self::linux::Kvm::new(cpu, ram)
-}
-
-#[cfg(target_os = "windows")]
-pub fn new(cpu: usize, ram: Arc<Ram>) -> Result<impl Hypervisor, VmmError> {
-    self::windows::Whp::new(cpu, ram)
-}
-
-#[cfg(target_os = "macos")]
-pub fn new(cpu: usize, ram: Arc<Ram>) -> Result<impl Hypervisor, VmmError> {
-    self::macos::Hf::new(cpu, ram)
-}
+#[cfg_attr(target_os = "linux", path = "linux/mod.rs")]
+#[cfg_attr(target_os = "macos", path = "macos/mod.rs")]
+#[cfg_attr(target_os = "windows", path = "windows/mod.rs")]
+mod os;
 
 /// Underlying hypervisor (e.g. KVM on Linux).
 pub trait Hypervisor: Send + Sync {
@@ -39,6 +21,8 @@ pub trait Hypervisor: Send + Sync {
     type CpuErr: Error + Send + 'static;
 
     fn cpu_features(&mut self) -> Result<CpuFeats, Self::CpuErr>;
+    fn ram(&self) -> &Ram;
+    fn ram_mut(&mut self) -> &mut Ram;
 
     /// This method must be called by a thread that is going to drive the returned CPU.
     fn create_cpu(&self, id: usize) -> Result<Self::Cpu<'_>, Self::CpuErr>;

src/core/src/vmm/hv/windows/mod.rs

@@ -1,7 +1,7 @@
 use self::cpu::WhpCpu;
 use self::partition::Partition;
 use super::{CpuFeats, Hypervisor};
-use crate::vmm::hw::Ram;
+use crate::vmm::ram::Ram;
 use crate::vmm::VmmError;
 use std::sync::Arc;
 use thiserror::Error;
@@ -10,16 +10,7 @@ use windows_sys::core::HRESULT;
 mod cpu;
 mod partition;
 
-/// Implementation of [`Hypervisor`] using Windows Hypervisor Platform.
-///
-/// Fields in this struct need to drop in a correct order.
-pub struct Whp {
-    part: Partition,
-    ram: Arc<Ram>,
-}
-
-impl Whp {
-    pub fn new(cpu: usize, ram: Arc<Ram>) -> Result<Self, VmmError> {
+pub fn new(cpu: usize, ram: Ram) -> Result<impl Hypervisor, VmmError> {
     // Setup a partition.
     let mut part = Partition::new().map_err(VmmError::CreatePartitionFailed)?;
 
@@ -31,8 +22,15 @@ impl Whp {
     part.map_gpa(ram.host_addr().cast(), 0, ram.len().try_into().unwrap())
         .map_err(VmmError::MapRamFailed)?;
 
-        Ok(Self { part, ram })
+    Ok(Whp { part, ram })
 }
+
+/// Implementation of [`Hypervisor`] using Windows Hypervisor Platform.
+///
+/// Fields in this struct need to drop in a correct order.
+struct Whp {
+    part: Partition,
+    ram: Ram,
 }
 
 impl Hypervisor for Whp {
@@ -43,6 +41,14 @@ impl Hypervisor for Whp {
         Ok(CpuFeats {})
     }
 
+    fn ram(&self) -> &Ram {
+        &self.ram
+    }
+
+    fn ram_mut(&mut self) -> &mut Ram {
+        &mut self.ram
+    }
+
     fn create_cpu(&self, id: usize) -> Result<Self::Cpu<'_>, Self::CpuErr> {
         let id = id.try_into().unwrap();
 

src/core/src/vmm/hw/console/context.rs

@@ -1,6 +1,7 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
 use super::Console;
-use crate::vmm::hv::{CpuIo, IoBuf};
-use crate::vmm::hw::{DeviceContext, Ram};
+use crate::vmm::hv::{CpuIo, Hypervisor, IoBuf};
+use crate::vmm::hw::DeviceContext;
 use crate::vmm::VmmEvent;
 use obvirt::console::{Memory, MsgType};
 use std::error::Error;
@@ -8,18 +9,18 @@ use std::mem::offset_of;
 use thiserror::Error;
 
 /// Implementation of [`DeviceContext`].
-pub struct Context<'a> {
+pub struct Context<'a, H> {
     dev: &'a Console,
-    ram: &'a Ram,
+    hv: &'a H,
     msg_len: usize,
     msg: String,
 }
 
-impl<'a> Context<'a> {
-    pub fn new(dev: &'a Console, ram: &'a Ram) -> Self {
+impl<'a, H: Hypervisor> Context<'a, H> {
+    pub fn new(dev: &'a Console, hv: &'a H) -> Self {
         Self {
             dev,
-            ram,
+            hv,
             msg_len: 0,
             msg: String::new(),
         }
@@ -75,14 +76,14 @@ impl<'a> Context<'a> {
             .map_err(|e| ExecError::TranslateVaddrFailed(vaddr, e))?;
 
         // Read data.
-        let data = unsafe { self.ram.host_addr().add(paddr) };
+        let data = unsafe { self.hv.ram().host_addr().add(paddr) };
         let data = unsafe { std::slice::from_raw_parts(data, len) };
 
         Ok(std::str::from_utf8(data).unwrap())
     }
 }
 
-impl<'a> DeviceContext for Context<'a> {
+impl<'a, H: Hypervisor> DeviceContext for Context<'a, H> {
     fn exec(&mut self, exit: &mut dyn CpuIo) -> Result<bool, Box<dyn Error>> {
         // Check field.
         let off = exit.addr() - self.dev.addr;

src/core/src/vmm/hw/console/mod.rs

@@ -1,5 +1,7 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
 use self::context::Context;
-use super::{Device, DeviceContext, Ram};
+use super::{Device, DeviceContext};
+use crate::vmm::hv::Hypervisor;
 use crate::vmm::VmmEventHandler;
 use obvirt::console::Memory;
 use std::num::NonZero;
@@ -26,7 +28,7 @@ impl Console {
     }
 }
 
-impl Device for Console {
+impl<H: Hypervisor> Device<H> for Console {
     fn addr(&self) -> usize {
         self.addr
     }
@@ -35,7 +37,7 @@ impl Device for Console {
         self.len
     }
 
-    fn create_context<'a>(&'a self, ram: &'a Ram) -> Box<dyn DeviceContext + 'a> {
-        Box::new(Context::new(self, ram))
+    fn create_context<'a>(&'a self, hv: &'a H) -> Box<dyn DeviceContext + 'a> {
+        Box::new(Context::new(self, hv))
     }
 }

src/core/src/vmm/hw/mod.rs

@@ -1,28 +1,29 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+use super::hv::{CpuIo, Hypervisor};
 use super::VmmEventHandler;
-use crate::vmm::hv::CpuIo;
 use std::collections::BTreeMap;
 use std::error::Error;
 use std::num::NonZero;
 use std::sync::Arc;
 
 pub use self::console::*;
-pub use self::ram::*;
 
 mod console;
-mod ram;
 
-pub fn setup_devices(
+pub fn setup_devices<H: Hypervisor>(
     start_addr: usize,
     block_size: NonZero<usize>,
     event: VmmEventHandler,
-) -> DeviceTree {
-    let mut map = BTreeMap::<usize, Arc<dyn Device>>::new();
+) -> DeviceTree<H> {
+    let mut map = BTreeMap::<usize, Arc<dyn Device<H>>>::new();
 
     // Console.
     let addr = start_addr;
     let console = Arc::new(Console::new(addr, block_size, event));
 
-    assert!(map.insert(console.addr(), console.clone()).is_none());
+    assert!(map
+        .insert(<Console as Device<H>>::addr(&console), console.clone())
+        .is_none());
 
     // Make sure nothing are overlapped.
     let mut end = start_addr;
@@ -36,31 +37,31 @@ pub fn setup_devices(
 }
 
 /// Contains all virtual devices, except RAM; for the VM.
-pub struct DeviceTree {
+pub struct DeviceTree<H: Hypervisor> {
     console: Arc<Console>,
-    map: BTreeMap<usize, Arc<dyn Device>>,
+    map: BTreeMap<usize, Arc<dyn Device<H>>>,
 }
 
-impl DeviceTree {
-    pub fn console(&self) -> &Console {
-        &self.console
+impl<H: Hypervisor> DeviceTree<H> {
+    pub fn console(&self) -> &impl Device<H> {
+        self.console.as_ref()
     }
 
     /// Returns iterator ordered by physical address.
-    pub fn map(&self) -> impl Iterator<Item = (usize, &dyn Device)> + '_ {
+    pub fn map(&self) -> impl Iterator<Item = (usize, &dyn Device<H>)> + '_ {
         self.map.iter().map(|(addr, dev)| (*addr, dev.as_ref()))
     }
 }
 
 /// Virtual device that has a physical address in the virtual machine.
-pub trait Device: Send + Sync {
+pub trait Device<H: Hypervisor>: Send + Sync {
     /// Physical address in the virtual machine.
     fn addr(&self) -> usize;
 
     /// Total size of device memory, in bytes.
     fn len(&self) -> NonZero<usize>;
 
-    fn create_context<'a>(&'a self, ram: &'a Ram) -> Box<dyn DeviceContext + 'a>;
+    fn create_context<'a>(&'a self, hv: &'a H) -> Box<dyn DeviceContext + 'a>;
 }
 
 /// Context to execute memory-mapped I/O operations on a virtual device.

src/core/src/vmm/mod.rs

@@ -1,9 +1,10 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 use self::hv::{Cpu, CpuExit, CpuFeats, CpuIo, Hypervisor};
-use self::hw::{setup_devices, Device, DeviceContext, DeviceTree, Ram, RamBuilder, RamMap};
+use self::hw::{setup_devices, Device, DeviceContext, DeviceTree};
 use self::kernel::{
     Kernel, PT_DYNAMIC, PT_GNU_EH_FRAME, PT_GNU_RELRO, PT_GNU_STACK, PT_LOAD, PT_NOTE, PT_PHDR,
 };
+use self::ram::{Ram, RamMap};
 use self::screen::Screen;
 use crate::error::RustError;
 use crate::profile::Profile;
@@ -28,6 +29,7 @@ mod arch;
 mod hv;
 mod hw;
 mod kernel;
+mod ram;
 mod screen;
 
 #[no_mangle]
@@ -312,16 +314,35 @@ pub unsafe extern "C" fn vmm_run(
         },
     };
 
-    // Setup RAM builder.
-    let mut ram = match RamBuilder::new(block_size) {
+    // Setup RAM.
+    let ram = match Ram::new(block_size) {
         Ok(v) => v,
         Err(e) => {
-            *err = RustError::wrap(e);
+            *err = RustError::with_source("couldn't create a RAM", e);
+            return null_mut();
+        }
+    };
+
+    // Setup hypervisor.
+    let mut hv = match self::hv::new(8, ram) {
+        Ok(v) => v,
+        Err(e) => {
+            *err = RustError::with_source("couldn't setup a hypervisor", e);
+            return null_mut();
+        }
+    };
+
+    // Load CPU features.
+    let feats = match hv.cpu_features() {
+        Ok(v) => v,
+        Err(e) => {
+            *err = RustError::with_source("couldn't get available vCPU features", e);
             return null_mut();
         }
     };
 
     // Map the kernel.
+    let mut ram = hv.ram_mut().builder();
     let kern = match ram.alloc_kernel(len) {
         Ok(v) => v,
         Err(e) => {
@@ -385,7 +406,7 @@ pub unsafe extern "C" fn vmm_run(
     }
 
     // Build RAM.
-    let (ram, map) = match ram.build(vm_page_size, &devices, dynamic) {
+    let map = match ram.build(vm_page_size, &devices, dynamic) {
         Ok(v) => v,
         Err(e) => {
             *err = RustError::with_source("couldn't build RAM", e);
@@ -393,25 +414,6 @@ pub unsafe extern "C" fn vmm_run(
         }
     };
 
-    // Setup hypervisor.
-    let ram = Arc::new(ram);
-    let mut hv = match self::hv::new(8, ram.clone()) {
-        Ok(v) => v,
-        Err(e) => {
-            *err = RustError::with_source("couldn't setup a hypervisor", e);
-            return null_mut();
-        }
-    };
-
-    // Load CPU features.
-    let feats = match hv.cpu_features() {
-        Ok(v) => v,
-        Err(e) => {
-            *err = RustError::with_source("couldn't get available vCPU features", e);
-            return null_mut();
-        }
-    };
-
     // Setup screen.
     let screen = match self::screen::Default::new(screen) {
         Ok(v) => v,
@@ -425,7 +427,6 @@ pub unsafe extern "C" fn vmm_run(
     let shutdown = Arc::new(AtomicBool::new(false));
     let args = CpuArgs {
         hv,
-        ram,
         screen: screen.buffer().clone(),
         feats,
         devices,
@@ -514,7 +515,7 @@ fn run_cpu<C: Cpu, H: Hypervisor>(mut cpu: C, args: &CpuArgs<H>) {
         .map(|(addr, dev)| {
             let end = dev.len().checked_add(addr).unwrap();
 
-            (addr, (dev.create_context(&args.ram), end))
+            (addr, (dev.create_context(&args.hv), end))
         })
         .collect::<BTreeMap<usize, (Box<dyn DeviceContext>, NonZero<usize>)>>();
 
@@ -666,19 +667,15 @@ impl From<MsgType> for VmmLog {
 /// Encapsulates arguments for a function to run a CPU.
 struct CpuArgs<H: Hypervisor> {
     hv: H,
-    ram: Arc<Ram>,
     screen: Arc<<self::screen::Default as Screen>::Buffer>,
     feats: CpuFeats,
-    devices: Arc<DeviceTree>,
+    devices: Arc<DeviceTree<H>>,
     shutdown: Arc<AtomicBool>,
 }
 
 /// Represents an error when [`vmm_new()`] fails.
 #[derive(Debug, Error)]
 enum VmmError {
-    #[error("couldn't create a RAM")]
-    CreateRamFailed(#[source] std::io::Error),
-
     #[cfg(target_os = "linux")]
     #[error("couldn't get maximum number of CPU for a VM")]
     GetMaxCpuFailed(#[source] std::io::Error),

src/core/src/vmm/ram/builder.rs

@@ -1,71 +1,31 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 use super::{Ram, RamError};
+use crate::vmm::hv::Hypervisor;
 use crate::vmm::hw::DeviceTree;
 use crate::vmm::kernel::ProgramHeader;
-use crate::vmm::VmmError;
 use obconf::{BootEnv, Config};
 use std::num::NonZero;
 use std::ops::Range;
 use thiserror::Error;
 
 /// Struct to build [`Ram`].
-pub struct RamBuilder {
-    ram: Ram,
+pub struct RamBuilder<'a> {
+    ram: &'a mut Ram,
     next: usize,
     kern: Option<Range<usize>>,
     stack: Option<Range<usize>>,
     args: Option<KernelArgs>,
 }
 
-impl RamBuilder {
-    /// # Safety
-    /// `block_size` must be greater or equal host page size.
-    pub unsafe fn new(block_size: NonZero<usize>) -> Result<Self, VmmError> {
-        use std::io::Error;
-
-        // Reserve memory range.
-        #[cfg(unix)]
-        let mem = {
-            use libc::{mmap, MAP_ANON, MAP_FAILED, MAP_PRIVATE, PROT_NONE};
-            use std::ptr::null_mut;
-
-            let mem = mmap(
-                null_mut(),
-                Ram::SIZE,
-                PROT_NONE,
-                MAP_PRIVATE | MAP_ANON,
-                -1,
-                0,
-            );
-
-            if mem == MAP_FAILED {
-                return Err(VmmError::CreateRamFailed(Error::last_os_error()));
-            }
-
-            mem.cast()
-        };
-
-        #[cfg(windows)]
-        let mem = {
-            use std::ptr::null;
-            use windows_sys::Win32::System::Memory::{VirtualAlloc, MEM_RESERVE, PAGE_NOACCESS};
-
-            let mem = VirtualAlloc(null(), Ram::SIZE, MEM_RESERVE, PAGE_NOACCESS);
-
-            if mem.is_null() {
-                return Err(VmmError::CreateRamFailed(Error::last_os_error()));
-            }
-
-            mem.cast()
-        };
-
-        Ok(Self {
-            ram: Ram { mem, block_size },
+impl<'a> RamBuilder<'a> {
+    pub(super) fn new(ram: &'a mut Ram) -> Self {
+        Self {
+            ram,
             next: 0,
             kern: None,
             stack: None,
             args: None,
-        })
+        }
     }
 
     /// # Panics
@@ -212,13 +172,13 @@ impl RamBuilder {
 }
 
 #[cfg(target_arch = "x86_64")]
-impl RamBuilder {
-    pub fn build(
+impl<'a> RamBuilder<'a> {
+    pub fn build<H: Hypervisor>(
         mut self,
         page_size: NonZero<usize>,
-        devices: &DeviceTree,
+        devices: &DeviceTree<H>,
         dynamic: ProgramHeader,
-    ) -> Result<(Ram, RamMap), RamBuilderError> {
+    ) -> Result<RamMap, RamBuilderError> {
         // Allocate page-map level-4 table. We use 4K 4-Level Paging here. You may wonder about this
         // because it seems like page size on the PS4 is 16K. The truth is the PS4 emulate the 16K
         // page size with 4K pages. You can check this by yourself by looking at
@@ -292,7 +252,7 @@ impl RamBuilder {
 
         unsafe { self.relocate_kernel(&map, dynamic, 8)? };
 
-        Ok((self.ram, map))
+        Ok(map)
     }
 
     fn setup_4k_page_tables(
@@ -393,17 +353,17 @@ impl RamBuilder {
 }
 
 #[cfg(target_arch = "aarch64")]
-impl RamBuilder {
+impl<'a> RamBuilder<'a> {
     const MA_DEV_NG_NR_NE: u8 = 0; // MEMORY_ATTRS[0]
     const MA_NOR: u8 = 1; // MEMORY_ATTRS[1]
     const MEMORY_ATTRS: [u8; 8] = [0, 0b11111111, 0, 0, 0, 0, 0, 0];
 
-    pub fn build(
+    pub fn build<H: Hypervisor>(
         mut self,
         page_size: NonZero<usize>,
-        devices: &DeviceTree,
+        devices: &DeviceTree<H>,
         dynamic: ProgramHeader,
-    ) -> Result<(Ram, RamMap), RamBuilderError> {
+    ) -> Result<RamMap, RamBuilderError> {
         // Setup page tables.
         let map = match page_size.get() {
             0x4000 => self.build_16k_page_tables(devices)?,
@@ -413,10 +373,13 @@ impl RamBuilder {
         // Relocate the kernel to virtual address.
         unsafe { self.relocate_kernel(&map, dynamic, 1027)? };
 
-        Ok((self.ram, map))
+        Ok(map)
     }
 
-    fn build_16k_page_tables(&mut self, devices: &DeviceTree) -> Result<RamMap, RamBuilderError> {
+    fn build_16k_page_tables<H: Hypervisor>(
+        &mut self,
+        devices: &DeviceTree<H>,
+    ) -> Result<RamMap, RamBuilderError> {
         // Allocate page table level 0.
         let page_table = self.next;
         let len = self.ram.block_size;

src/core/src/vmm/ram/mod.rs

@@ -22,6 +22,50 @@ pub struct Ram {
 impl Ram {
     pub(crate) const SIZE: usize = 1024 * 1024 * 1024 * 8; // 8GB
 
+    /// # Safety
+    /// `block_size` must be greater or equal host page size.
+    pub unsafe fn new(block_size: NonZero<usize>) -> Result<Self, Error> {
+        use std::io::Error;
+
+        // Reserve memory range.
+        #[cfg(unix)]
+        let mem = {
+            use libc::{mmap, MAP_ANON, MAP_FAILED, MAP_PRIVATE, PROT_NONE};
+            use std::ptr::null_mut;
+
+            let mem = mmap(
+                null_mut(),
+                Self::SIZE,
+                PROT_NONE,
+                MAP_PRIVATE | MAP_ANON,
+                -1,
+                0,
+            );
+
+            if mem == MAP_FAILED {
+                return Err(Error::last_os_error());
+            }
+
+            mem.cast()
+        };
+
+        #[cfg(windows)]
+        let mem = {
+            use std::ptr::null;
+            use windows_sys::Win32::System::Memory::{VirtualAlloc, MEM_RESERVE, PAGE_NOACCESS};
+
+            let mem = VirtualAlloc(null(), Self::SIZE, MEM_RESERVE, PAGE_NOACCESS);
+
+            if mem.is_null() {
+                return Err(Error::last_os_error());
+            }
+
+            mem.cast()
+        };
+
+        Ok(Self { mem, block_size })
+    }
+
     pub fn host_addr(&self) -> *const u8 {
         self.mem
     }
@@ -30,6 +74,10 @@ impl Ram {
         Self::SIZE
     }
 
+    pub fn builder(&mut self) -> RamBuilder {
+        RamBuilder::new(self)
+    }
+
     /// # Panics
     /// If `addr` or `len` is not multiply by block size.
     ///

src/core/src/vmm/x86_64.rs

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 use super::hv::{Cpu, CpuFeats, CpuStates};
-use super::hw::RamMap;
+use super::ram::RamMap;
 use super::MainCpuError;
 
 pub fn setup_main_cpu(