On Mon, 18 Dec 2023 13:03:32 +0000 "Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx> wrote: > On Wed, Dec 13, 2023 at 12:50:38PM +0000, Russell King wrote: > > From: James Morse <james.morse@xxxxxxx> > > > > acpi_processor_get_info() registers all present CPUs. Registering a > > CPU is what creates the sysfs entries and triggers the udev > > notifications. > > > > arm64 virtual machines that support 'virtual cpu hotplug' use the > > enabled bit to indicate whether the CPU can be brought online, as > > the existing ACPI tables require all hardware to be described and > > present. > > > > If firmware describes a CPU as present, but disabled, skip the > > registration. Such CPUs are present, but can't be brought online for > > whatever reason. (e.g. firmware/hypervisor policy). > > > > Once firmware sets the enabled bit, the CPU can be registered and > > brought online by user-space. Online CPUs, or CPUs that are missing > > an _STA method must always be registered. > > ... > > > @@ -526,6 +552,9 @@ static void acpi_processor_post_eject(struct acpi_device *device) > > acpi_processor_make_not_present(device); > > return; > > } > > + > > + if (cpu_present(pr->id) && !(sta & ACPI_STA_DEVICE_ENABLED)) > > + arch_unregister_cpu(pr->id); > > This change isn't described in the commit log, but seems to be the cause > of the build error identified by the kernel build bot that is fixed > later in this series. I'm wondering whether this should be in a > different patch, maybe "ACPI: Check _STA present bit before making CPUs > not present" ? Would seem a bit odd to call arch_unregister_cpu() way before the code is added to call the matching arch_registers_cpu() Mind you this eject doesn't just apply to those CPUs that are registered later I think, but instead to all. So we run into the spec hole that there is no way to identify initially 'enabled' CPUs that might be disabled later. > > Or maybe my brain isn't working properly (due to being Covid positive.) > Any thoughts, Jonathan? I'll go with a resounding 'not sure' on where this change belongs. I blame my non existent start of the year hangover. Hope you have recovered! Jonathan
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