There are cases where a guest tries to switch spinlocks to bare metal behavior (e.g. by setting "xen_nopvspin" on XEN platform and "hv_nopvspin" on HYPER_V). That feature is missed on KVM, add a new parameter "nopvspin" to disable PV spinlocks for KVM guest. The new 'nopvspin' parameter will also replace Xen and Hyper-V specific parameters in future patches. Define variable nopvsin as global because it will be used in future patches as above. Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Radim Krcmar <rkrcmar@xxxxxxxxxx> Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Cc: Wanpeng Li <wanpengli@xxxxxxxxxxx> Cc: Jim Mattson <jmattson@xxxxxxxxxx> Cc: Joerg Roedel <joro@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> --- Documentation/admin-guide/kernel-parameters.txt | 5 +++++ arch/x86/include/asm/qspinlock.h | 1 + arch/x86/kernel/kvm.c | 21 ++++++++++++++------- kernel/locking/qspinlock.c | 7 +++++++ 4 files changed, 27 insertions(+), 7 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index c7ac2f3..89d77ea 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5330,6 +5330,11 @@ as generic guest with no PV drivers. Currently support XEN HVM, KVM, HYPER_V and VMWARE guest. + nopvspin [X86,KVM] + Disables the qspinlock slow path using PV optimizations + which allow the hypervisor to 'idle' the guest on lock + contention. + xirc2ps_cs= [NET,PCMCIA] Format: <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index 444d6fd..d86ab94 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -32,6 +32,7 @@ static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lo extern void __pv_init_lock_hash(void); extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock); +extern bool nopvspin; #define queued_spin_unlock queued_spin_unlock /** diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index e820568..481d879 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -831,16 +831,23 @@ __visible bool __kvm_vcpu_is_preempted(long cpu) */ void __init kvm_spinlock_init(void) { - /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ - if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) - return; - - if (kvm_para_has_hint(KVM_HINTS_REALTIME)) + /* + * Don't use the pvqspinlock code if no KVM_FEATURE_PV_UNHALT feature + * support, or there is REALTIME hints or only 1 vCPU. + */ + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT) || + kvm_para_has_hint(KVM_HINTS_REALTIME) || + num_possible_cpus() == 1) { + pr_info("PV spinlocks disabled\n"); return; + } - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ - if (num_possible_cpus() == 1) + if (nopvspin) { + pr_info("PV spinlocks disabled forced by \"nopvspin\" parameter.\n"); + static_branch_disable(&virt_spin_lock_key); return; + } + pr_info("PV spinlocks enabled\n"); __pv_init_lock_hash(); pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 2473f10..75193d6 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -580,4 +580,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) #include "qspinlock_paravirt.h" #include "qspinlock.c" +bool nopvspin __initdata; +static __init int parse_nopvspin(char *arg) +{ + nopvspin = true; + return 0; +} +early_param("nopvspin", parse_nopvspin); #endif -- 1.8.3.1