linux/arch/x86/kernel/cpu/perfctr-watchdog.c

// SPDX-License-Identifier: GPL-2.0
/*
 * local apic based NMI watchdog for various CPUs.
 *
 * This file also handles reservation of performance counters for coordination
 * with other users.
 *
 * Note that these events normally don't tick when the CPU idles. This means
 * the frequency varies with CPU load.
 *
 * Original code for K7/P6 written by Keith Owens
 *
 */

#include <linux/percpu.h>
#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/bitops.h>
#include <linux/smp.h>
#include <asm/nmi.h>
#include <linux/kprobes.h>

#include <asm/apic.h>
#include <asm/perf_event.h>

/*
 * this number is calculated from Intel's MSR_P4_CRU_ESCR5 register and it's
 * offset from MSR_P4_BSU_ESCR0.
 *
 * It will be the max for all platforms (for now)
 */
#define NMI_MAX_COUNTER_BITS …

/*
 * perfctr_nmi_owner tracks the ownership of the perfctr registers:
 * evtsel_nmi_owner tracks the ownership of the event selection
 * - different performance counters/ event selection may be reserved for
 *   different subsystems this reservation system just tries to coordinate
 *   things a little
 */
static DECLARE_BITMAP(perfctr_nmi_owner, NMI_MAX_COUNTER_BITS);
static DECLARE_BITMAP(evntsel_nmi_owner, NMI_MAX_COUNTER_BITS);

/* converts an msr to an appropriate reservation bit */
static inline unsigned int nmi_perfctr_msr_to_bit(unsigned int msr)
{ … }

/*
 * converts an msr to an appropriate reservation bit
 * returns the bit offset of the event selection register
 */
static inline unsigned int nmi_evntsel_msr_to_bit(unsigned int msr)
{ … }

int reserve_perfctr_nmi(unsigned int msr)
{ … }
EXPORT_SYMBOL(…);

void release_perfctr_nmi(unsigned int msr)
{ … }
EXPORT_SYMBOL(…);

int reserve_evntsel_nmi(unsigned int msr)
{ … }
EXPORT_SYMBOL(…);

void release_evntsel_nmi(unsigned int msr)
{ … }
EXPORT_SYMBOL(…);