Summary We use Virtualization.framework to run macOS guests on Apple silicon. When the guest is updated from macOS 15.6.1 to 15.8.1 inside the VM, the update writes a new boot loader, mBoot-20457.1.29, into the VM's auxiliary storage. After the update, the guest kernel can use only about 1.75 GB of the configured memory. The kernel wires the rest as VM_KERN_COUNT_BOOT_STOLEN. The guest swaps all the time, and builds become 7 to 18 times slower. The fault stays after a cold boot. The guest boot-args value is empty. Environment Host: macOS 26.7.2 (25G320), Apple M3 Pro, 36 GB Guest before the update: macOS 15.6.1 (24G90), installed from the IPSW Guest after the update: macOS 15.8.1 (24H32), installed with softwareupdate inside the guest VM configuration: VZMacOSBootLoader with the default ROM, VZMacPlatformConfiguration, VZMacAuxiliaryStorage, memorySize = 15032385536 (14 GiB), CPUCount = 6 A customer sees the same fault on macOS 26.6.2 with an M2 Pro host. Steps to reproduce Create a macOS 15.6.1 VM from the IPSW. Set memory to 14 GiB. Boot the guest and confirm the RAM. vm_stat accounts for about 14 GiB. In the guest, run: sudo softwareupdate --install "macOS Sequoia 15.8.1-24H32" --restart --agree-to-license --user <owner> --stdinpass After the guest restarts, run sudo zprint | grep BOOT_STOLEN and vm_stat. Shut down the VM, start it again, and do step 4 again. Expected result The guest can use about 14 GiB of RAM, as it could before the update. Actual result 15.6.1, before the update 15.8.1, after the update and after a cold boot hw.memsize 15032385536 15032385536 RAM accounted for by vm_stat (free + active + inactive + speculative + wired + compressor) about 13.99 GiB about 1.75 GiB VM_KERN_COUNT_BOOT_STOLEN not measured 12,845,072 KB (about 12.25 GiB) Swap activity Swapins 0, Swapouts 0 Swapins 225,835, Swapouts 267,316 nvram boot-args empty empty Auxiliary storage contents after the update The auxiliary storage has two boot loader slots. Each slot has a 16-byte HUFA header: magic, version, upgrade count, and slot offset from 0x4000. Header offset Upgrade count Slot offset Boot loader 0x4000 1 0x24000 iBoot-11881.140.96 (the original 15.6.1 boot loader) 0x5000 2 0x224000 mBoot-20457.1.29 (written by the 15.8.1 update) The VM boots the slot with the higher count, which is mBoot-20457.1.29. Workaround test (customer) The customer worked on a copy of an affected VM. They copied the iBoot-11881.140.96 slot over the active mBoot-20457.1.29 slot in the auxiliary storage. macOS 15.8.1 then booted with about 14 GB of usable RAM, and the RAM stayed correct after cold boots. Their results: Extraction and validation of nine Xcode versions: 9 to 10 minutes (it was 68 to 102 minutes). Xcode 26.1.1 simulator installation and cache preparation: under 7 minutes (it was more than 2 hours). This workaround changes Apple's signed firmware by hand... Not really a good idea. Related report A public report describes the same fault with UTM and the same boot loader version. It also says that the kernel computes the stolen value from the memSizeActual and memSize boot parameters that the boot loader supplies. The author filed FB24992831 (https://wadetregaskis.com/the-macos-sequoia-15-8-updater-stole-my-ram/) Questions Is this a known fault in mBoot-20457.1.29? Will a later update fix it? Is there a supported way to make a VM boot a specific boot loader slot? Or a supported way to roll back the boot loader in VZMacAuxiliaryStorage? Is there a configuration on the host or in the guest that makes mBoot pass the full memory size? We'd prefer to not make nvram read only if the new mBoot is absolutely needed for some reason.

Hi, we're only seeing 15.6.1 IPSW available for VMs. Where can we find latest and secure versions of macOS IPSW on https://updates.cdn-apple.com/*/fullrestores/ ? Is there an official list somewhere that Apple provides? We need to be sure we can create the latest 15.7.7 VMs with automation and not rely on inner VM upgrades of MacOS.

The language in the new EULA seems to indicate we can get permission to run more than 2 VMs on a single host. "(iii) except as otherwise provided in writing, signed, or issued by an authorized representative of Apple, to install, use and run up to two (2) additional copies or instances of the Apple Software, or any prior macOS or OS X operating system software or subsequent release of the Apple Software, within virtual operating system environments on each Apple-branded computer you own or control that is already running the Apple Software, for purposes of: (a) software development; (b) testing during software development; (c) using macOS Server; or (d) personal, non-commercial use." This is important because we often have use-cases that require running docker containers and other Virtualization tools along-side of two VMs on the host and obviously cant. What's the steps we can take to get written permission for this? Thank you!

Hi, we're seeing a panic when we SIGSTOP the logd pid. panic(cpu 2 caller 0xfffffe0020e9a364): userspace watchdog timeout: no successful checkins from logd (0 induced crashes) in 120 seconds You may ask "well why would you do that?" and the answer is that we're seeing panics from watchdog/logd when we hammer the diskIO for a download/write (APFS sparse file creation) operation in our software. Is it normal to see this?

Hi, I installed Xcode 27 beta 2 and now I can't create any VMs using Virtualization. I tried uninstalling the beta Xcode and re-installing the Xcode 26, but it's still failing. I was able to create VMs using ipsws before I installed Xcode 27, so I'm certain it's the cause. Is there a way to fully uninstall everything having to do with Xcode from the machine without having to re-install my entire macOS?

We're seeing limitations in host -> macOS VM changes syncing. Were using Anka, but we've also tried others. We're actually doing the exact implementation that others (the ones we found that are open source) do. Here is a breakdown of what's supported: Operation Direction Supported Notes Create new file/folder Host → Guest ✅ Yes New paths appear in the guest Create new file/folder Guest → Host ✅ Yes New paths appear on the host Read existing contents Host → Guest ✅ Yes Contents present at mount time are visible Modify file in place Guest → Host ✅ Yes Guest edits are written through to the host Modify file in place Host → Guest ❌ No Guest keeps stale contents for already-accessed files (macOS virtiofs caching) Delete file/folder Guest → Host ✅ Yes Removal is reflected on the host Delete file/folder Host → Guest ❌ No Guest still sees the path after the host deletes it (cached) Replace via temp + rename() (atomic) Host → Guest ✅ Yes New inode/dentry; recommended way to update files from the host We're requesting a way to disable caching and/or allow the unsupported actions in the table to be supported. https://feedbackassistant.apple.com/feedback/22905515

We see a major delay for the first open("disk.img", O_RDONLY); we perform. If it helps, we use clonefile() to copy a sparsed image. if (-1 == (fd = open(path, (mode & O_ACCMODE) | O_CLOEXEC))) return -1; 1791 Thread_1071327 DispatchQueue_1: com.apple.main-thread (serial) 1791 start (in dyld) + 6076 [0x189f72b98] 1791 main (in anka_image) + 20 [0x102171bb8] 1791 clp_main (in libpolicy.dylib) + 2120 [0x102a49eac] 1790 process_info (in anka_image) + 68 [0x1021723f4] + 1790 vdsk_open (in libvdsk.dylib) + 92 [0x1021d90e8] + 1790 vdsk_open_native (in libvdsk.dylib) + 164 [0x1021d91c0] + 1790 open (in libsystem_kernel.dylib) + 64 [0x18a2dd6a4] + 1790 __open (in libsystem_kernel.dylib) + 8 [0x18a2d2678] What advice do you have for diagnosing what is causing the first open to do this? Is this some sort of security scan happening? Indexing?

In the latest 26.5, when creating a VM we can no longer disable SIP. We have confirmed we're using the proper admin user (anka) and its proper password (same one we log into the GUI with). It just keeps asking for the password as if it's wrong. It's critical we can disable SIP for VMs like we have been in previous versions.

Hi, is there any ETA on when we can see support for nested virtualization in MacOS VMs? Running Docker specifically would be nice.

Hi, I have two issues going on: Creation of macOS VMs requires autologin is enabled: Mon Apr 13 11:27:18 20 anka.log (ankahv) 511: pid 511: installing /Users/veertu/Library/Application Support/Veertu/Anka/img_lib/UniversalMac_15.6.1_24G90_Restore.ipsw... Mon Apr 13 11:27:20 40 anka.log (install) 511: (null): installation failed: Error Domain=VZErrorDomain Code=10007 "The virtual machine failed to start." UserInfo={NSLocalizedFailure=An error occurred during installation., NSLocalizedFailureReason=The virtual machine failed to start., NSUnderlyingError=0xca2c0ced0 {Error Domain=VZErrorDomain Code=-9 "The virtual machine encountered a security error." UserInfo={NSLocalizedFailure=Unable to access security information., NSLocalizedFailureReason=The virtual machine encountered a security error., NSUnderlyingError=0xca3029320 {Error Domain=NSPOSIXErrorDomain Code=22 "Invalid argument" UserInfo={NSLocalizedFailureReason=Failed to get current host key., NSUnderlyingError=0xca30292f0 {Error Domain=NSPOSIXErrorDomain Code=22 "Invalid argument" UserInfo=0xca2a88040 (not displayed)}}}}}} Mon Apr 13 11:27:20 40 anka.log (install) 511: (null): virtual machine stopped with error: Error Domain=VZErrorDomain Code=4 "Transition from state “error” to state “stopping” is invalid." UserInfo={NSLocalizedFailure=Invalid virtual machine state transition., NSLocalizedFailureReason=Transition from state “error” to state “stopping” is invalid.} Mon Apr 13 11:27:20 40 anka.log (install) 511: failed to install macOS: Error Domain=VZErrorDomain Code=10007 "The virtual machine failed to start." UserInfo={NSLocalizedFailure=An error occurred during installation., NSLocalizedFailureReason=The virtual machine failed to start., NSUnderlyingError=0xca2c0ced0 {Error Domain=VZErrorDomain Code=-9 "The virtual machine encountered a security error." UserInfo={NSLocalizedFailure=Unable to access security information., NSLocalizedFailureReason=The virtual machine encountered a security error., NSUnderlyingError=0xca3029320 {Error Domain=NSPOSIXErrorDomain Code=22 "Invalid argument" UserInfo={NSLocalizedFailureReason=Failed to get current host key., NSUnderlyingError=0xca30292f0 {Error Domain=NSPOSIXErrorDomain Code=22 "Invalid argument" UserInfo=0xca2a88040 (not displayed)}}}}}} Running a macOS 26.x VM fails for similar reasons, yet running a 15.x VM works fine: Mon Apr 13 11:20:10 20 0f5d4fe7-edac-4f6d-aebb-f185702f2c25.log (ankahv) 474: pid 474: session started on host 26.4.1 Mon Apr 13 11:20:10 40 0f5d4fe7-edac-4f6d-aebb-f185702f2c25.log (ankahv) 474: 0f5d4fe7-edac-4f6d-aebb-f185702f2c25: failed to start: Error Domain=VZErrorDomain Code=-9 "The virtual machine encountered a security error." UserInfo={NSLocalizedFailure=Unable to access security information., NSLocalizedFailureReason=The virtual machine encountered a security error., NSUnderlyingError=0x76f049e00 {Error Domain=NSPOSIXErrorDomain Code=22 "Invalid argument" UserInfo={NSLocalizedFailureReason=Failed to get current host key., NSUnderlyingError=0x76f049e60 {Error Domain=NSPOSIXErrorDomain Code=22 "Invalid argument" UserInfo={NSLocalizedFailureReason=Failed to create new HostKey., NSUnderlyingError=0x76f049dd0 {Error Domain=NSPOSIXErrorDomain Code=22 "Invalid argument" UserInfo=0x76ec49d60 (not displayed)}}}}}} Mon Apr 13 11:20:10 40 0f5d4fe7-edac-4f6d-aebb-f185702f2c25.log (ankanet) 474: failed to receive packets: Connection reset by peer This is super painful for us to manage since some of our users can't have autologin enabled (like major banks under strict MDM requirements). Or, AWS EC2 Macs which have no VNC enabled at all by default. What's the trick here to make sure we can consistently use virtualization without autologin?

We're trying to create 26.4 beta and RC VMs on 15.x and 26.3 host OS' without success. We see Tue Mar 17 17:27:36 40 anka.log (install) 45803: failed to install macOS: Error Domain=VZErrorDomain Code=10006 "Installation requires a software update." UserInfo={NSLocalizedFailure=A software update is required to complete the installation., NSLocalizedFailureReason=Installation requires a software update.} Yet, if we create it the same way on 26.4 beta host OS, it works. We've tried the usual tricks of installing latest Xcode and preparing it (accepting license, etc). But, they don't work on 26.3 and 15.x. What's the trick to get the creation of 26.4 to work on <= 26.3 host OS?

I'm trying to find the installer for Metal Toolchain 26. It seems to fix an issue I have but I don't want to have to install Xcode 26 just to get the toolchain installed. Is this possible?

We're seeing a pretty big problem with 15.x hosts and using SSH to execute builds. Yet this works just fine in the terminal over VNC. We see similar limitations with SSH and Virtualization too. They look related, but don't know. Xcode 16.4 15.4.1 Host OS Mac Mini M1. Let me know what else is needed. + xcodebuild -workspace /Users/veertu/anka-arm/./Anka.xcworkspace . . . build build /Users/veertu/anka-arm/build/Build/Products/Release/libpolicy.dylib: errSecInternalComponent Command CodeSign failed with a nonzero exit code ** BUILD FAILED ** /Users/veertu/anka-arm/build/Build/Products/Release/libpolicy.dylib: errSecInternalComponent Command CodeSign failed with a nonzero exit code ** BUILD FAILED ** Watching the Console logs I see . . . codesign CSSM Exception: -2147415840 CSSMERR_CSP_NO_USER_INTERACTION codesign error while checking integrity, denying access: CSSM CSSMERR_CSP_NO_USER_INTERACTION error 14:53:57.404848-0500 codesign SecKeyCreateSignature failed: Error Domain=NSOSStatusErrorDomain Code=-25308 "CSSM Exception: -2147415840 CSSMERR_CSP_NO_USER_INTERACTION" (errKCInteractionNotAllowed / errSecInteractionNotAllowed: / Interaction is not allowed with the Security Server.) UserInfo={numberOfErrorsDeep=0, NSDescription=CSSM Exception: -2147415840 CSSMERR_CSP_NO_USER_INTERACTION} default 14:53:57.405567-0500 codesign MacOS error: -2070 . . .

The VM gets a NAT IP just fine, but it doesn't have access through the proxy so I'm guessing 15.x macOS setup has a bug where it can't break out of a loop trying to phone home back to macOS. FBID: FB15689777 This is not an issue for 14.x VMs. It's also seen across different Virtualization tools.

https://feedbackassistant.apple.com/feedback/15645457 Metal passthrough on intel VMs causes com.apple.screensharing.menuextra to crash and screensharing to exit Create a 15.1 VM with metal passthrough on 15.0.1 or 15.1 host, enable Screen Sharing, then try connecting to with VNC after restarting the machine. I'm using Anka to create the VM. You'll see VNC work (open vnc://192.168.64.3:5900), then a few seconds in show "Reconnecting...", then work, then go to "Reconnecting..." for ~5m until it eventually works consistently. You'll see launchd showing exits/failures (see screenshots) You'll see diagnostic reports showing things like: Thread 0 Crashed:: Dispatch queue: com.apple.RenderBox.Encoder 0 libsystem_kernel.dylib 0x7ff801da5b52 __pthread_kill + 10 1 libsystem_pthread.dylib 0x7ff801ddff85 pthread_kill + 262 2 libsystem_c.dylib 0x7ff801d00b19 abort + 126 3 libsystem_c.dylib 0x7ff801cffddc __assert_rtn + 314 4 Metal 0x7ff80d045d72 MTLReportFailure.cold.1 + 41 5 Metal 0x7ff80d01fa2a MTLReportFailure + 513 6 Metal 0x7ff80cfb74e0 +[MTLLoader sliceIDForDevice:legacyDriverVersion:airntDriverVersion:] + 200 7 Metal 0x7ff80cf265c9 +[_MTLBinaryArchive(MTLBinaryArchiveInternal) deserializeBinaryArchiveHeader:fileData:device:] + 89 8 Metal 0x7ff80cf10f0c -[_MTLBinaryArchive loadFromURL:error:] + 537 9 Metal 0x7ff80cf10288 -[_MTLBinaryArchive initWithOptions:device:url:error:] + 844 10 RenderBox 0x7ff9041a15fd RB::(anonymous namespace)::load_library_archive(NSBundle*,