x86/multikernel: explain spawn timer initialization · multikernel/linux@4e05ab7 · GitHub

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nickolaev

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x86/multikernel: explain spawn timer initialization

Spawn kernels do not own the PIT, PIC, or IO-APIC resources. The X86_SUBARCH_MULTIKERNEL platform quirk therefore leaves timer_init and wallclock_init as no-ops so an instance never programs host timer hardware or requests IRQ0. setup_percpu_clockev() initializes the local APIC timer for instance ticks. Keeping global_clock_event unset bypasses LAPIC timer verification, whose fallback path requires the unavailable legacy IRQ0. Document that timer path next to the platform quirk. Signed-off-by: Nikolay Nikolaev <nicknickolaev@gmail.com>

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‎arch/x86/kernel/platform-quirks.c‎

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Original file line number	Diff line number	Diff line change
@@ -172,7 +172,9 @@ void __init x86_early_init_platform_quirks(void)
172	172	* the PIT - which belongs to the host - and then request
173	173	* legacy IRQ0, which can never reach an instance CPU that
174	174	* has neither a PIC nor an IO-APIC. Ticks come from the
175		- * local APIC timer via setup_percpu_clockev() instead.
	175	+ * local APIC timer initialized by setup_percpu_clockev().
	176	+ * Keeping global_clock_event unset bypasses LAPIC timer
	177	+ * verification, whose fallback path requires legacy IRQ0.
176	178	*/
177	179	x86_init.timers.timer_init = x86_init_noop;
178	180	x86_init.timers.wallclock_init = x86_init_noop;

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