arch, vmm: Enable initramfs on AArch64

Ported Firecracker commit 144b6c.

Signed-off-by: Michael Zhao <michael.zhao@arm.com>

arch/src/aarch64/mod.rs

@@ -35,8 +35,8 @@ pub enum Error {
     /// Failed to create a GIC.
     SetupGIC(gic::Error),
 
-    /// Failed to compute the initrd address.
-    InitrdAddress,
+    /// Failed to compute the initramfs address.
+    InitramfsAddress,
 
     /// Error configuring the general purpose registers
     REGSConfiguration(regs::Error),
@@ -165,6 +165,26 @@ pub fn configure_system<T: DeviceInfoForFDT + Clone + Debug>(
     Ok(())
 }
 
+/// Returns the memory address where the initramfs could be loaded.
+pub fn initramfs_load_addr(
+    guest_mem: &GuestMemoryMmap,
+    initramfs_size: usize,
+) -> super::Result<u64> {
+    let round_to_pagesize = |size| (size + (super::PAGE_SIZE - 1)) & !(super::PAGE_SIZE - 1);
+    match GuestAddress(get_fdt_addr(&guest_mem))
+        .checked_sub(round_to_pagesize(initramfs_size) as u64)
+    {
+        Some(offset) => {
+            if guest_mem.address_in_range(offset) {
+                Ok(offset.raw_value())
+            } else {
+                Err(super::Error::AArch64Setup(Error::InitramfsAddress))
+            }
+        }
+        None => Err(super::Error::AArch64Setup(Error::InitramfsAddress)),
+    }
+}
+
 /// Returns the memory address where the kernel could be loaded.
 pub fn get_kernel_start() -> u64 {
     layout::RAM_64BIT_START

arch/src/lib.rs

@@ -88,8 +88,8 @@ pub mod aarch64;
 #[cfg(target_arch = "aarch64")]
 pub use aarch64::{
     arch_memory_regions, configure_system, configure_vcpu, fdt::DeviceInfoForFDT,
-    get_host_cpu_phys_bits, get_kernel_start, layout, layout::CMDLINE_MAX_SIZE, layout::IRQ_BASE,
-    layout::IRQ_MAX, EntryPoint,
+    get_host_cpu_phys_bits, get_kernel_start, initramfs_load_addr, layout,
+    layout::CMDLINE_MAX_SIZE, layout::IRQ_BASE, layout::IRQ_MAX, EntryPoint,
 };
 
 #[cfg(target_arch = "x86_64")]