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authorChristian Krinitsin <mail@krinitsin.com>2025-06-01 21:35:14 +0200
committerChristian Krinitsin <mail@krinitsin.com>2025-06-01 21:35:14 +0200
commit3e4c5a6261770bced301b5e74233e7866166ea5b (patch)
tree9379fddaba693ef8a045da06efee8529baa5f6f4 /gitlab/issues_text/target_missing/host_missing/accel_missing/2705
parente5634e2806195bee44407853c4bf8776f7abfa4f (diff)
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clean up repository
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-USB event delivery does not work correctly for macOS guests with XHCI controller without MSI(-X)
-Steps to reproduce:
-1. Get a macOS VM working. Either on x86-64 with a Q35 machine type, AppleSMC device, and OpenCore bootloader, or on aarch64 using the patch set and instructions linked above.
-2. On x86-64, switch to a NEC XHCI controller with MSI and MSI-X support forcibly disabled: `-device nec-usb-xhci,id=xhci,msi=off,msix=off`
-3. Boot macOS.
-
-USB events are now extremely laggy. A USB keyboard or mouse becomes almost unusable.
-
-
-While narrowing down the problem, I established the following facts by experimentation, tracing, and code inspection:
-
- * Although the vmapple platform uses an emulated XHCI PCI device for connecting virtual USB devices, it does not support message-signalled interrupts, in either the MSI or MSI-X persuasion. (This is true in Apple's implementation as well, but the macOS guest's XHCI driver unsurprisingly does work with Apple's PCI/XHCI implementation.)
- * macOS guests (and the iBoot bootloader) appear to refuse to drive XHCI controllers with `numintrs < 4`, for both aarch64 and x86-64 architectures. They will generally set up event rings 0, 1, and 2.
- * QEMU's PCI XHCI implementation does not appear to implement (as of 9.2.0-rc2) any mitigations for when the controller is used in pin-based IRQ mode. It will happily attempt to use event rings >0 in this case, but interrupts are dropped.
- * Linux and FreeBSD guests appear to use only interrupter 0 anyway, so these are not useful references.
-
-It's not entirely clear to me what component is ultimately responsible for the failure here - I suspect there might be some not-quite-right behaviour in both macOS's XHCI driver and Qemu's XHCI implementation, and that these conspire to a non-functional setup.