Core2Again v0.1.1-rc2

Core2Again v0.1.1-rc2

This release candidate addresses OpenCore multiboot. A Dell T9300 user confirmed that v0.1.1-rc1 fixed Windows 11 restart, then reported that globally loading Core2Again prevented macOS and Linux Mint from booting.

Core2Again now checks the EFI image calling ExitBootServices. It enters VMX for the normal Windows boot manager (bootmgfw.efi), loader (winload.efi), and resume loader (winresume.efi). Other loaders continue on the physical CPU. The check is allocation-free so it does not invalidate the loader's memory-map key.

This recognizes Windows boot loaders, not Windows 11 24H2 specifically. Older Windows releases using these paths also activate Core2Again. For exact per-entry control, continue using the OpenCore Tools method. The change has passed KVM tests but has not yet been confirmed on the reporter's Dell laptops.

Checks

• A host test accepts Windows loader paths and rejects Linux, macOS, fallback, and malformed paths.
• With SSE4.2 masked in KVM, a Windows-like EFI loader enters VMX and sees the advertised feature; a generic EFI loader remains native. Forcing the old unconditional behavior makes the non-Windows test fail.
• A two-core Windows 11 image reached the desktop through the SeaBIOS/OpenDuet USB image in KVM. QEMU does not exercise Penryn's unsupported-instruction emulation or reproduce the Dell multiboot issue.
• All four driver variants passed the host-instruction, VMX handoff, and diagnostic-mode checks. The previous boot-processor INIT reset regression also passed under KVM.

Trying it with OpenCore

Back up the working EFI file and OpenCore configuration. Replace the configured driver with Core2Again-RELEASE.efi, using the filename expected by your configuration. Keep only one loaded copy; do not also launch it from Tools on the same boot. Test Linux Mint and macOS first, then Windows 11, both cores, and Restart. The multiboot guide has fallback and reporting steps.

SHA256SUMS covers every attached binary and the license notice archive. GitHub's source archive for this tag contains the matching source.

Core2Again v0.1.1-rc1

Core2Again v0.1.1-rc1

Experimental restart update for legacy BIOS systems. Two Dell T9300 users reported that Windows 11 24H2 runs and shuts down, but freezes on a black screen during restart.

Core2Again previously parked the boot processor in wait-for-SIPI when it received INIT. That can leave the machine frozen during a reset. This build requests a chipset reset in that case. Application processor INIT-SIPI startup is unchanged.

The Dell restart issue is not yet confirmed fixed on hardware. The reporter's machines still need to test this build.

What we checked

• A new two-processor KVM test deliberately sends INIT to the boot processor. The v0.1.0 handler fails the test; this build resets cleanly.
• The same test passes with EPT disabled, matching the older Penryn memory path.
• The KVM application processor startup test passes.
• The RELEASE and DEBUG EFI binaries pass the host-instruction and VMX handoff checks.
• A Windows restart in QEMU succeeded even with the old driver, so that run cannot confirm the Dell symptom.

Trying it

Back up the Core2Again EFI file currently loaded by OpenCore. Replace it with Core2Again-RELEASE.efi from this release, using the filename your configuration expects. Boot Windows, then try Restart from the Start menu. The restart troubleshooting guide lists the details that would help if it still freezes. Core2Again-DEBUG.efi can show checkpoint 31 if a boot-processor INIT reaches the new reset path but the chipset does not reset.

The compressed USB images contain this driver and the same OpenDuet boot chain as v0.1.0. SHA256SUMS covers every attached binary and the license notice archive. GitHub's source archives contain the matching source commit.

Core2Again v0.1.0

Core2Again v0.1.0

First public source release of Core2Again, the UEFI VMX driver for running Windows 11 on older Intel Core 2 processors. It reports SSE4.2 and POPCNT to the guest, then emulates instructions the physical CPU lacks. SSE4.1 emulation is included for Conroe and Kentsfield processors.

This is a prerelease. An earlier Clover-based diagnostic build reached a Windows 11 desktop on a physical Core 2 Duo T9900 with both cores visible. The EFI files and OpenDuet USB images attached here have been built and tested under QEMU/KVM, but have not yet been booted on that physical machine.

Downloads

• Core2Again-RELEASE.efi: normal driver, with screen diagnostics compiled out.
• Core2Again-DEBUG.efi: driver with on-screen checkpoints and counters.
• Core2Again-singlecore.efi: fallback that leaves other processors alone.
• Core2Again-apdebug.efi: AP startup diagnostic build.
• Core2AgainLoader.efi: loads the driver and Windows Boot Manager.
• core2again-legacy-blockio.img.gz: recommended USB image for a legacy BIOS, using BIOS disk access.
• core2again-legacy-native.img.gz: USB image using OpenDuet's native storage drivers.
• Core2Again-v0.1.0-notices.zip: Core2Again, EDK II, and OpenCore license texts.
• SHA256SUMS: hashes for all of the above.

GitHub also provides the source code as a ZIP and tarball below the assets. The README covers setup; the legacy boot guide covers writing a USB stick and checking a boot failure.

Checks completed

• Differential emulator suite: 41,179,296 comparisons, zero mismatches.
• KVM AP trampoline test: one application processor reached C.
• Static verification: all five EFI variants passed their applicable checks; an intentionally altered RELEASE binary was rejected.
• SeaBIOS/KVM boot with a preinstalled Windows 11 image: reached the desktop with two virtual CPUs; the per-vCPU kernel check passed.

A QEMU/KVM boot on the development Xeon does not exercise the #UD emulation path because that host executes SSE4.2 directly. The physical T9900 release-image boot remains the next validation step.