Implement map_file_cow before a sandbox is initialised

[simongdavies]

Overview

This pull request implements map_file_cow on UninitializedSandbox so file mappings can be created before a VM exists.

It refactors the file mapping logic for guest sandboxes, splitting the process into two distinct phases: host-side preparation and VM-side application. The main goal is to allow file mappings to be prepared before the VM exists and then applied any later when the VM is created (i.e., during evolve).

Changes

• File Mapping Refactor and Modularization:

  • Added file_mapping module and PreparedFileMapping abstraction for two-phase file mapping (host-side preparation and VM-side application), with safe cleanup and platform-specific handling.
  • Refactored MultiUseSandbox::map_file_cow to use the new abstraction, removing duplicated platform-specific code.

• Support for Deferred File Mapping:

  • Added pending_file_mappings to UninitializedSandbox and a new map_file_cow method to defer mapping until VM creation.

• Code Cleanup and Dependency Updates:

  • Removed obsolete imports and platform-specific code from initialized_multi_use.rs, consolidating logic in file_mapping.

• Test and API Adaptations:

  • Updated call sites and tests to use the new file mapping API and pass page_size as needed.

Also fixes a bug where the mmap memory access flags were too permissive (remove wx for KVM and x for mshv)

[Copilot]

Pull request overview

Implements deferred map_file_cow for UninitializedSandbox by introducing a two-phase host-prepare / VM-apply file mapping flow, enabling mappings to be created before VM initialization and applied during evolve.

Changes:

• Added sandbox::file_mapping with PreparedFileMapping to encapsulate host OS mapping resources with RAII cleanup.
• Added pending_file_mappings to UninitializedSandbox plus a new map_file_cow that prepares mappings pre-VM and applies them during evolve.
• Refactored MultiUseSandbox::map_file_cow to use the new shared preparation path and added tests for deferred mapping behavior.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/hyperlight_host/src/sandbox/uninitialized_evolve.rs	Applies deferred prepared mappings before vm.initialise(); threads page size into VM setup.
src/hyperlight_host/src/sandbox/uninitialized.rs	Stores pending prepared mappings and exposes UninitializedSandbox::map_file_cow.
src/hyperlight_host/src/sandbox/mod.rs	Exposes new file_mapping module.
src/hyperlight_host/src/sandbox/initialized_multi_use.rs	Refactors map_file_cow to use shared preparation; adds deferred-mapping tests.
src/hyperlight_host/src/sandbox/file_mapping.rs	New module implementing PreparedFileMapping, OS-specific preparation, and RAII cleanup.
src/hyperlight_host/src/hypervisor/mod.rs	Updates tests/call sites to pass page size into hypervisor setup.
src/hyperlight_host/src/hypervisor/hyperlight_vm/x86_64.rs	Plumbs page size into HyperlightVm::new and removes setting it in initialise.

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[danbugs]

Two minor non-blocking NITs you might want to look at. Otherwise LGTM.

[danbugs]

LGTM