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// 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/paravirt.h>
#include <asm/apic.h>
static bool __initdata hv_pvspin = 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 rdmsrl() 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 rdmsrl() when the lock state has not changed.
*/
if (READ_ONCE(*byte) == val) {
unsigned long msr_val;
rdmsrl(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);
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