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13c4d4626a
Fixes the following W=1 kernel build warning(s): arch/x86/hyperv/hv_spinlock.c:28:16: warning: variable ‘msr_val’ set but not used [-Wunused-but-set-variable] unsigned long msr_val; As Hypervisor Top-Level Functional Specification states in chapter 7.5 Virtual Processor Idle Sleep State, "A partition which possesses the AccessGuestIdleMsr privilege (refer to section 4.2.2) may trigger entry into the virtual processor idle sleep state through a read to the hypervisor-defined MSR HV_X64_MSR_GUEST_IDLE". That means only a read of the MSR is necessary. The returned value msr_val is not used. Cast it to void to silence this warning. Reference: https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs Reported-by: Hulk Robot <hulkci@huawei.com> Signed-off-by: Xu Yihang <xuyihang@huawei.com> Link: https://lore.kernel.org/r/20210323024302.174434-1-xuyihang@huawei.com Signed-off-by: Wei Liu <wei.liu@kernel.org>
92 lines
2.2 KiB
C
92 lines
2.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Hyper-V specific spinlock code.
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*
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* Copyright (C) 2018, Intel, Inc.
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*
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* Author : Yi Sun <yi.y.sun@intel.com>
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*/
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#define pr_fmt(fmt) "Hyper-V: " fmt
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#include <linux/spinlock.h>
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#include <asm/mshyperv.h>
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#include <asm/paravirt.h>
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#include <asm/apic.h>
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static bool __initdata hv_pvspin = true;
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static void hv_qlock_kick(int cpu)
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{
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apic->send_IPI(cpu, X86_PLATFORM_IPI_VECTOR);
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}
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static void hv_qlock_wait(u8 *byte, u8 val)
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{
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unsigned long flags;
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if (in_nmi())
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return;
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/*
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* Reading HV_X64_MSR_GUEST_IDLE MSR tells the hypervisor that the
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* vCPU can be put into 'idle' state. This 'idle' state is
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* terminated by an IPI, usually from hv_qlock_kick(), even if
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* interrupts are disabled on the vCPU.
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*
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* To prevent a race against the unlock path it is required to
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* disable interrupts before accessing the HV_X64_MSR_GUEST_IDLE
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* MSR. Otherwise, if the IPI from hv_qlock_kick() arrives between
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* the lock value check and the rdmsrl() then the vCPU might be put
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* into 'idle' state by the hypervisor and kept in that state for
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* an unspecified amount of time.
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*/
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local_irq_save(flags);
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/*
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* Only issue the rdmsrl() when the lock state has not changed.
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*/
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if (READ_ONCE(*byte) == val) {
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unsigned long msr_val;
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rdmsrl(HV_X64_MSR_GUEST_IDLE, msr_val);
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(void)msr_val;
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}
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local_irq_restore(flags);
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}
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/*
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* Hyper-V does not support this so far.
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*/
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__visible bool hv_vcpu_is_preempted(int vcpu)
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{
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return false;
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}
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PV_CALLEE_SAVE_REGS_THUNK(hv_vcpu_is_preempted);
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void __init hv_init_spinlocks(void)
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{
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if (!hv_pvspin || !apic ||
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!(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
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!(ms_hyperv.features & HV_MSR_GUEST_IDLE_AVAILABLE)) {
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pr_info("PV spinlocks disabled\n");
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return;
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}
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pr_info("PV spinlocks enabled\n");
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__pv_init_lock_hash();
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pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
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pv_ops.lock.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
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pv_ops.lock.wait = hv_qlock_wait;
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pv_ops.lock.kick = hv_qlock_kick;
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pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(hv_vcpu_is_preempted);
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}
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static __init int hv_parse_nopvspin(char *arg)
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{
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hv_pvspin = false;
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return 0;
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}
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early_param("hv_nopvspin", hv_parse_nopvspin);
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