Extract low level UFFD handler to a separate package

[ValentaTomas]

• Extract low level UFFD handler to a separate package
• Remove unused struct
• Improve uffd tests (ensure they are not flaky)
  • Add the 2M hugpages tests

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Note

Extracts UFFD logic into a new userfaultfd package with memory mapping abstractions, updates orchestrator integration, and adds comprehensive tests and helpers.

• Refactor UFFD handling:
  • Move low-level logic into packages/orchestrator/internal/sandbox/uffd/userfaultfd with a userfaultfd wrapper (Serve, Register, AddWriteProtection, Close, copy).
  • Replace mapping with memory module: introduce MemoryMap interface and MemfileMap with GetOffset; update Firecracker mapping to package memory.
  • Update orchestrator uffd.go to use memory.MemfileMap and the new userfaultfd instance (fd management via wrapper, Serve method); add writeProtection field.
  • Tweak UFFD constants/bindings (add UFFDIO_COPY_MODE_DONTWAKE, UFFDIO_WAKE; adjust address types and copy dst handling).
• Testing:
  • Add testutils (contiguous map, mmap creators, test data helpers).
  • Add userfaultfd tests for missing, write-protect, combined modes, and cross-process double registration.

^{Written by Cursor Bugbot for commit 67b1bfb. This will update automatically on new commits. Configure here.}

[ValentaTomas]

I'll improve the tests a little, but the rest should be ready.

[Copilot]

Pull Request Overview

This PR extracts the low-level user fault file descriptor (UFFD) handler into a separate userfaultfd package, improving code organization and modularity. The extraction refactors the UFFD functionality out of the main uffd package into a dedicated userfaultfd subpackage.

• Moved UFFD handling logic from uffd package to new userfaultfd package
• Created abstraction layer with memory mapping interfaces
• Added comprehensive test coverage for UFFD functionality including cross-process scenarios

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/orchestrator/internal/sandbox/uffd/userfaultfd/userfaultfd_test.go	Comprehensive test suite for UFFD missing page and write protection scenarios
packages/orchestrator/internal/sandbox/uffd/userfaultfd/userfaultfd_cross_process_test.go	Cross-process UFFD tests simulating FC-orchestrator interaction
packages/orchestrator/internal/sandbox/uffd/userfaultfd/userfaultfd.go	Core UFFD operations including registration and copy functionality
packages/orchestrator/internal/sandbox/uffd/userfaultfd/serve.go	UFFD event handling and page fault processing logic
packages/orchestrator/internal/sandbox/uffd/userfaultfd/constants.go	UFFD constants and helper functions with improved address handling
packages/orchestrator/internal/sandbox/uffd/uffd.go	Updated to use new userfaultfd package and memory interfaces
packages/orchestrator/internal/sandbox/uffd/testutils/	Test utilities for memory mapping and data preparation
packages/orchestrator/internal/sandbox/uffd/memory/	Memory mapping interfaces and Firecracker-specific implementations

Comments suppressed due to low confidence (2)

packages/orchestrator/internal/sandbox/uffd/userfaultfd/constants.go:1

• The constant UFFD_FEATURE_WP_HUGETLBFS_SHMEM is being removed but may be needed for write protection features. Verify this removal is intentional and doesn't break functionality.

package userfaultfd

packages/orchestrator/internal/sandbox/uffd/uffd.go:1

• The TrackAndReturnNil method is being removed. Ensure all callers of this method have been updated to handle its removal.

package uffd

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[ValentaTomas]

bugbot run

[cursor]

✅ Bugbot reviewed your changes and found no bugs!

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[ValentaTomas]

✅ Extracted all non-relevant (mostly write-protection and direct memory access related) code to separate PRs so it can be merged in steps.

[djeebus]

Looks good! Just added some opinions, none of which are critical.