x86/multikernel: isolate LAPIC timer policy · multikernel/linux@b715339 · GitHub

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Commit b715339

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nickolaev

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x86/multikernel: isolate LAPIC timer policy

Keep spawned kernels from rejecting their calibrated LAPIC timer. The host-owned platform timer cannot advance local jiffies. Keep the policy in arch/x86/multikernel and one predicate in APIC code. Signed-off-by: Nikolay Nikolaev <nicknickolaev@gmail.com>

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4 files changed

+31-2Lines changed: 31 additions & 2 deletions

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• arch/x86
  • include/asm
    • multikernel.h
  • kernel/apic
    • apic.c
  • multikernel
    • Makefile
    • timer.c

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‎arch/x86/include/asm/multikernel.h‎

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+5Lines changed: 5 additions & 0 deletions

Original file line number	Diff line number	Diff line change
@@ -71,11 +71,16 @@ struct mk_pci_host_bridge;
71	71
72	72	#ifdef CONFIG_MULTIKERNEL
73	73	void __init x86_multikernel_pci_platform_init(void);
	74	+ bool x86_multikernel_skip_apic_timer_verify(void);
74	75	int mk_arch_snapshot_pci_host_bridges(const struct mk_instance *instance,
75	76	struct mk_pci_host_bridge *bridges,
76	77	size_t capacity);
77	78	#else
78	79	static inline void x86_multikernel_pci_platform_init(void) { }
	80	+ static inline bool x86_multikernel_skip_apic_timer_verify(void)
	81	+ {
	82	+ return false;
	83	+ }
79	84	#endif
80	85
81	86	#endif /* __ASSEMBLY__ */

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‎arch/x86/kernel/apic/apic.c‎

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+3-1Lines changed: 3 additions & 1 deletion

Original file line number	Diff line number	Diff line change
@@ -67,6 +67,7 @@
67	67	#include <asm/intel-family.h>
68	68	#include <asm/irq_regs.h>
69	69	#include <asm/cpu.h>
	70	+ #include <asm/multikernel.h>
70	71
71	72	#include "local.h"
72	73
@@ -923,7 +924,8 @@ static int __init calibrate_APIC_clock(void)
923	924	* timer based calibration, if a global clockevent device is
924	925	* available.
925	926	*/
926		- if (!pm_referenced && global_clock_event) {
	927	+ if (!pm_referenced && global_clock_event &&
	928	+ !x86_multikernel_skip_apic_timer_verify()) {
927	929	apic_pr_verbose("... verify APIC timer\n");
928	930
929	931	/*

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‎arch/x86/multikernel/Makefile‎

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+1-1Lines changed: 1 addition & 1 deletion

Original file line number	Diff line number	Diff line change
@@ -3,4 +3,4 @@
3	3	# Makefile for multikernel spawn support
4	4	#
5	5
6		- obj-y += spawn.o pci.o direct_boot.o head_64.o
	6	+ obj-y += spawn.o pci.o timer.o direct_boot.o head_64.o

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‎arch/x86/multikernel/timer.c‎

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+22Lines changed: 22 additions & 0 deletions

Original file line number	Diff line number	Diff line change
@@ -0,0 +1,22 @@
	1	+ // SPDX-License-Identifier: GPL-2.0-only
	2	+ /* x86 timer policy for multikernel spawn kernels. */
	3	+
	4	+ #include <linux/printk.h>
	5	+
	6	+ #include <asm/bootparam.h>
	7	+ #include <asm/multikernel.h>
	8	+ #include <asm/setup.h>
	9	+
	10	+ bool x86_multikernel_skip_apic_timer_verify(void)
	11	+ {
	12	+ if (boot_params.hdr.hardware_subarch != X86_SUBARCH_MULTIKERNEL)
	13	+ return false;
	14	+
	15	+ /*
	16	+ * A spawn kernel does not own the platform timer interrupt used by the
	17	+ * legacy verification. Its LAPIC was calibrated against the TSC, while
	18	+ * jiffies driven by the primary kernel's timer cannot advance here.
	19	+ */
	20	+ pr_info("APIC timer: skipping legacy timer verification for multikernel\n");
	21	+ return true;
	22	+ }

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