1 // SPDX-License-Identifier: GPL-2.0 2 3 /* 4 * Hyper-V specific spinlock code. 5 * 6 * Copyright (C) 2018, Intel, Inc. 7 * 8 * Author : Yi Sun <yi.y.sun@intel.com> 9 */ 10 11 #define pr_fmt(fmt) "Hyper-V: " fmt 12 13 #include <linux/spinlock.h> 14 15 #include <asm/mshyperv.h> 16 #include <asm/paravirt.h> 17 #include <asm/apic.h> 18 19 static bool __initdata hv_pvspin = true; 20 21 static void hv_qlock_kick(int cpu) 22 { 23 apic->send_IPI(cpu, X86_PLATFORM_IPI_VECTOR); 24 } 25 26 static void hv_qlock_wait(u8 *byte, u8 val) 27 { 28 unsigned long flags; 29 30 if (in_nmi()) 31 return; 32 33 /* 34 * Reading HV_X64_MSR_GUEST_IDLE MSR tells the hypervisor that the 35 * vCPU can be put into 'idle' state. This 'idle' state is 36 * terminated by an IPI, usually from hv_qlock_kick(), even if 37 * interrupts are disabled on the vCPU. 38 * 39 * To prevent a race against the unlock path it is required to 40 * disable interrupts before accessing the HV_X64_MSR_GUEST_IDLE 41 * MSR. Otherwise, if the IPI from hv_qlock_kick() arrives between 42 * the lock value check and the rdmsrl() then the vCPU might be put 43 * into 'idle' state by the hypervisor and kept in that state for 44 * an unspecified amount of time. 45 */ 46 local_irq_save(flags); 47 /* 48 * Only issue the rdmsrl() when the lock state has not changed. 49 */ 50 if (READ_ONCE(*byte) == val) { 51 unsigned long msr_val; 52 53 rdmsrl(HV_X64_MSR_GUEST_IDLE, msr_val); 54 55 (void)msr_val; 56 } 57 local_irq_restore(flags); 58 } 59 60 /* 61 * Hyper-V does not support this so far. 62 */ 63 __visible bool hv_vcpu_is_preempted(int vcpu) 64 { 65 return false; 66 } 67 PV_CALLEE_SAVE_REGS_THUNK(hv_vcpu_is_preempted); 68 69 void __init hv_init_spinlocks(void) 70 { 71 if (!hv_pvspin || !apic || 72 !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) || 73 !(ms_hyperv.features & HV_MSR_GUEST_IDLE_AVAILABLE)) { 74 pr_info("PV spinlocks disabled\n"); 75 return; 76 } 77 pr_info("PV spinlocks enabled\n"); 78 79 __pv_init_lock_hash(); 80 pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; 81 pv_ops.lock.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); 82 pv_ops.lock.wait = hv_qlock_wait; 83 pv_ops.lock.kick = hv_qlock_kick; 84 pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(hv_vcpu_is_preempted); 85 } 86 87 static __init int hv_parse_nopvspin(char *arg) 88 { 89 hv_pvspin = false; 90 return 0; 91 } 92 early_param("hv_nopvspin", hv_parse_nopvspin); 93