From 05eee619ed61c8cd89633954d38c4e5653086845 Mon Sep 17 00:00:00 2001 From: Zhenzhong Duan Date: Wed, 23 Oct 2019 19:16:22 +0800 Subject: [PATCH] x86/kvm: Add "nopvspin" parameter to disable PV spinlocks 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 Reviewed-by: Vitaly Kuznetsov Cc: Jonathan Corbet Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: "H. Peter Anvin" Cc: Paolo Bonzini Cc: Radim Krcmar Cc: Sean Christopherson Cc: Vitaly Kuznetsov Cc: Wanpeng Li Cc: Jim Mattson Cc: Joerg Roedel Cc: Peter Zijlstra Cc: Will Deacon Signed-off-by: Paolo Bonzini --- .../admin-guide/kernel-parameters.txt | 5 +++ arch/x86/include/asm/qspinlock.h | 1 + arch/x86/kernel/kvm.c | 43 +++++++++++++++---- kernel/locking/qspinlock.c | 7 +++ 4 files changed, 47 insertions(+), 9 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index fb95fad81c79..6a8934ffdaf6 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5739,6 +5739,11 @@ 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: ,,,,,[,[,[,]]] diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index 444d6fd9a6d8..d86ab942219c 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -32,6 +32,7 @@ extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); 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 4ef21a87f1d3..d9995931ea18 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -871,18 +871,36 @@ asm( */ 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)) { - static_branch_disable(&virt_spin_lock_key); + /* + * In case host doesn't support KVM_FEATURE_PV_UNHALT there is still an + * advantage of keeping virt_spin_lock_key enabled: virt_spin_lock() is + * preferred over native qspinlock when vCPU is preempted. + */ + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) { + pr_info("PV spinlocks disabled, no host support\n"); return; } - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ - if (num_possible_cpus() == 1) - return; + /* + * Disable PV spinlocks and use native qspinlock when dedicated pCPUs + * are available. + */ + if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints\n"); + goto out; + } + + if (num_possible_cpus() == 1) { + pr_info("PV spinlocks disabled, single CPU\n"); + goto out; + } + + if (nopvspin) { + pr_info("PV spinlocks disabled, forced by \"nopvspin\" parameter\n"); + goto out; + } + + pr_info("PV spinlocks enabled\n"); __pv_init_lock_hash(); pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; @@ -895,6 +913,13 @@ void __init kvm_spinlock_init(void) pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(__kvm_vcpu_is_preempted); } + /* + * When PV spinlock is enabled which is preferred over + * virt_spin_lock(), virt_spin_lock_key's value is meaningless. + * Just disable it anyway. + */ +out: + static_branch_disable(&virt_spin_lock_key); } #endif /* CONFIG_PARAVIRT_SPINLOCKS */ diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index b9515fcc9b29..cbff6ba53d56 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -581,4 +581,11 @@ EXPORT_SYMBOL(queued_spin_lock_slowpath); #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