// SPDX-License-Identifier: GPL-2.0

/*
 * Hyper-V specific spinlock code.
 *
 * Copyright (C) 2018, Intel, Inc.
 *
 * Author : Yi Sun <yi.y.sun@intel.com>
 */

#define pr_fmt(fmt) "Hyper-V: " fmt

#include <linux/spinlock.h>

#include <asm/mshyperv.h>
#include <asm/apic.h>
#include <asm/msr.h>

static bool hv_pvspin __initdata = true;

static void hv_qlock_kick(int cpu)
{
        __apic_send_IPI(cpu, X86_PLATFORM_IPI_VECTOR);
}

static void hv_qlock_wait(u8 *byte, u8 val)
{
        unsigned long flags;

        if (in_nmi())
                return;

        /*
         * Reading HV_X64_MSR_GUEST_IDLE MSR tells the hypervisor that the
         * vCPU can be put into 'idle' state. This 'idle' state is
         * terminated by an IPI, usually from hv_qlock_kick(), even if
         * interrupts are disabled on the vCPU.
         *
         * To prevent a race against the unlock path it is required to
         * disable interrupts before accessing the HV_X64_MSR_GUEST_IDLE
         * MSR. Otherwise, if the IPI from hv_qlock_kick() arrives between
         * the lock value check and the rdmsrq() then the vCPU might be put
         * into 'idle' state by the hypervisor and kept in that state for
         * an unspecified amount of time.
         */
        local_irq_save(flags);
        /*
         * Only issue the rdmsrq() when the lock state has not changed.
         */
        if (READ_ONCE(*byte) == val) {
                unsigned long msr_val;

                rdmsrq(HV_X64_MSR_GUEST_IDLE, msr_val);

                (void)msr_val;
        }
        local_irq_restore(flags);
}

/*
 * Hyper-V does not support this so far.
 */
__visible bool hv_vcpu_is_preempted(int vcpu)
{
        return false;
}

PV_CALLEE_SAVE_REGS_THUNK(hv_vcpu_is_preempted);

void __init hv_init_spinlocks(void)
{
        if (!hv_pvspin || !apic ||
            !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
            !(ms_hyperv.features & HV_MSR_GUEST_IDLE_AVAILABLE)) {
                pr_info("PV spinlocks disabled\n");
                return;
        }
        pr_info("PV spinlocks enabled\n");

        __pv_init_lock_hash();
        pv_ops_lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
        pv_ops_lock.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
        pv_ops_lock.wait = hv_qlock_wait;
        pv_ops_lock.kick = hv_qlock_kick;
        pv_ops_lock.vcpu_is_preempted = PV_CALLEE_SAVE(hv_vcpu_is_preempted);
}

static __init int hv_parse_nopvspin(char *arg)
{
        hv_pvspin = false;
        return 0;
}
early_param("hv_nopvspin", hv_parse_nopvspin);