// 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 msr_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) rdmsrl(HV_X64_MSR_GUEST_IDLE, 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_X64_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);