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authorChristian Krinitsin <mail@krinitsin.com>2025-05-21 21:21:26 +0200
committerChristian Krinitsin <mail@krinitsin.com>2025-05-21 21:21:26 +0200
commit4b927bc37359dec23f67d3427fc982945f24f404 (patch)
tree245449ef9146942dc7fffd0235b48b7e70a00bf2 /gitlab/issues/target_missing/host_missing/accel_missing/2705.toml
parentaa8bd79cec7bf6790ddb01d156c2ef2201abbaab (diff)
downloademulator-bug-study-4b927bc37359dec23f67d3427fc982945f24f404.tar.gz
emulator-bug-study-4b927bc37359dec23f67d3427fc982945f24f404.zip
add gitlab issues in toml format
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+id = 2705
+title = "USB event delivery does not work correctly for macOS guests with XHCI controller without MSI(-X)"
+state = "closed"
+created_at = "2024-12-01T15:45:07.801Z"
+closed_at = "2025-03-06T05:32:11.312Z"
+labels = ["USB", "hostos: macOS"]
+url = "https://gitlab.com/qemu-project/qemu/-/issues/2705"
+host-os = "Any"
+host-arch = "x86-64, aarch64"
+qemu-version = "9.2.0-rc2"
+guest-os = "macOS"
+guest-arch = "x86-64, aarch64"
+description = "n/a"
+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."""
+additional = "n/a"