Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...
[muen/linux.git] / arch / x86 / hyperv / hv_spinlock.c
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 msr_val;
29         unsigned long flags;
30
31         if (in_nmi())
32                 return;
33
34         /*
35          * Reading HV_X64_MSR_GUEST_IDLE MSR tells the hypervisor that the
36          * vCPU can be put into 'idle' state. This 'idle' state is
37          * terminated by an IPI, usually from hv_qlock_kick(), even if
38          * interrupts are disabled on the vCPU.
39          *
40          * To prevent a race against the unlock path it is required to
41          * disable interrupts before accessing the HV_X64_MSR_GUEST_IDLE
42          * MSR. Otherwise, if the IPI from hv_qlock_kick() arrives between
43          * the lock value check and the rdmsrl() then the vCPU might be put
44          * into 'idle' state by the hypervisor and kept in that state for
45          * an unspecified amount of time.
46          */
47         local_irq_save(flags);
48         /*
49          * Only issue the rdmsrl() when the lock state has not changed.
50          */
51         if (READ_ONCE(*byte) == val)
52                 rdmsrl(HV_X64_MSR_GUEST_IDLE, msr_val);
53         local_irq_restore(flags);
54 }
55
56 /*
57  * Hyper-V does not support this so far.
58  */
59 bool hv_vcpu_is_preempted(int vcpu)
60 {
61         return false;
62 }
63 PV_CALLEE_SAVE_REGS_THUNK(hv_vcpu_is_preempted);
64
65 void __init hv_init_spinlocks(void)
66 {
67         if (!hv_pvspin || !apic ||
68             !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
69             !(ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)) {
70                 pr_info("PV spinlocks disabled\n");
71                 return;
72         }
73         pr_info("PV spinlocks enabled\n");
74
75         __pv_init_lock_hash();
76         pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
77         pv_ops.lock.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
78         pv_ops.lock.wait = hv_qlock_wait;
79         pv_ops.lock.kick = hv_qlock_kick;
80         pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(hv_vcpu_is_preempted);
81 }
82
83 static __init int hv_parse_nopvspin(char *arg)
84 {
85         hv_pvspin = false;
86         return 0;
87 }
88 early_param("hv_nopvspin", hv_parse_nopvspin);