Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx> writes: > 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, 30 insertions(+), 4 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 ef836d6..6e14bd4 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -825,18 +825,31 @@ __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)) > + /* > + * Disable PV qspinlocks if host kernel doesn't support > + * KVM_FEATURE_PV_UNHALT feature or there is only 1 vCPU. > + * virt_spin_lock_key is enabled to avoid lock holder > + * preemption issue. > + */ > + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT) || > + num_possible_cpus() == 1) { > + pr_info("PV spinlocks disabled\n"); Why don't we need static_branch_disable(&virt_spin_lock_key) here? Also, as you're printing the exact reason for PV spinlocks disablement in other cases, I'd suggest separating "no host support" and "single CPU" cases. > return; > + } > > if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { > + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints.\n"); > static_branch_disable(&virt_spin_lock_key); > 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"); Nit: to make it sound better a comma is missing between 'disabled' and 'forced', or "PV spinlocks forcefully disabled by ..." if you prefer. > + 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 -- Vitaly