diff options
| author | Zhenzhong Duan <zhenzhong.duan@oracle.com> | 2019-10-23 14:16:22 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-07-08 23:21:57 +0300 |
| commit | 05eee619ed61c8cd89633954d38c4e5653086845 (patch) | |
| tree | 2e535cff34fd3d57031fcdcb30882ec65266ae6c /arch/x86/kernel/kvm.c | |
| parent | 5aefd786fba7336c1ecc608e2a126e4f45b180d7 (diff) | |
| download | linux-05eee619ed61c8cd89633954d38c4e5653086845.tar.xz | |
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 <zhenzhong.duan@oracle.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krcmar <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kernel/kvm.c')
| -rw-r--r-- | arch/x86/kernel/kvm.c | 39 |
1 files changed, 32 insertions, 7 deletions
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)) + /* + * 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; + } + /* + * Disable PV spinlocks and use native qspinlock when dedicated pCPUs + * are available. + */ if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { - static_branch_disable(&virt_spin_lock_key); - return; + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints\n"); + goto out; } - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ - if (num_possible_cpus() == 1) - return; + 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 */ |