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 hv_pvspin __initdata = 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
68 PV_CALLEE_SAVE_REGS_THUNK(hv_vcpu_is_preempted);
69
70 void __init hv_init_spinlocks(void)
71 {
72 if (!hv_pvspin || !apic ||
73 !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
74 !(ms_hyperv.features & HV_MSR_GUEST_IDLE_AVAILABLE)) {
75 pr_info("PV spinlocks disabled\n");
76 return;
77 }
78 pr_info("PV spinlocks enabled\n");
79
80 __pv_init_lock_hash();
81 pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
82 pv_ops.lock.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
83 pv_ops.lock.wait = hv_qlock_wait;
84 pv_ops.lock.kick = hv_qlock_kick;
85 pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(hv_vcpu_is_preempted);
86 }
87
88 static __init int hv_parse_nopvspin(char *arg)
89 {
90 hv_pvspin = false;
91 return 0;
92 }
93 early_param("hv_nopvspin", hv_parse_nopvspin);
94
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