From 196f20ca52e8c7281932663c348fa54b82d03914 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Tue, 28 Jun 2016 14:54:19 +0800 Subject: [PATCH] KVM: vmx: fix missed cancellation of TSC deadline timer MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit INFO: rcu_sched detected stalls on CPUs/tasks: 1-...: (11800 GPs behind) idle=45d/140000000000000/0 softirq=0/0 fqs=21663 (detected by 0, t=65016 jiffies, g=11500, c=11499, q=719) Task dump for CPU 1: qemu-system-x86 R running task 0 3529 3525 0x00080808 ffff8802021791a0 ffff880212895040 0000000000000001 00007f1c2c00db40 ffff8801dd20fcd3 ffffc90002b98000 ffff8801dd20fc88 ffff8801dd20fcf8 0000000000000286 ffff8801dd2ac538 ffff8801dd20fcc0 ffffffffc06949c9 Call Trace: ? kvm_write_guest_cached+0xb9/0x160 [kvm] ? __delay+0xf/0x20 ? wait_lapic_expire+0x14a/0x200 [kvm] ? kvm_arch_vcpu_ioctl_run+0xcbe/0x1b00 [kvm] ? kvm_arch_vcpu_ioctl_run+0xe34/0x1b00 [kvm] ? kvm_vcpu_ioctl+0x2d3/0x7c0 [kvm] ? __fget+0x5/0x210 ? do_vfs_ioctl+0x96/0x6a0 ? __fget_light+0x2a/0x90 ? SyS_ioctl+0x79/0x90 ? do_syscall_64+0x7c/0x1e0 ? entry_SYSCALL64_slow_path+0x25/0x25 This can be reproduced readily by running a full dynticks guest(since hrtimer in guest is heavily used) w/ lapic_timer_advance disabled. If fail to program hardware preemption timer, we will fallback to hrtimer based method, however, a previous programmed preemption timer miss to cancel in this scenario which results in one hardware preemption timer and one hrtimer emulated tsc deadline timer run simultaneously. So sometimes the target guest deadline tsc is earlier than guest tsc, which leads to the computation in vmx_set_hv_timer can underflow and cause delta_tsc to be set a huge value, then host soft lockup as above. This patch fix it by cancelling the previous programmed preemption timer if there is once we failed to program the new preemption timer and fallback to hrtimer based method. Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Yunhong Jiang Signed-off-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.c | 48 ++++++++++++++++++++++---------------------- 1 file changed, 24 insertions(+), 24 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 9c20ac14caf5..22a6474af220 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1366,27 +1366,35 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu) } EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer); +static bool start_hv_tscdeadline(struct kvm_lapic *apic) +{ + u64 tscdeadline = apic->lapic_timer.tscdeadline; + + if (atomic_read(&apic->lapic_timer.pending) || + kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) { + if (apic->lapic_timer.hv_timer_in_use) + cancel_hv_tscdeadline(apic); + } else { + apic->lapic_timer.hv_timer_in_use = true; + hrtimer_cancel(&apic->lapic_timer.timer); + + /* In case the sw timer triggered in the window */ + if (atomic_read(&apic->lapic_timer.pending)) + cancel_hv_tscdeadline(apic); + } + trace_kvm_hv_timer_state(apic->vcpu->vcpu_id, + apic->lapic_timer.hv_timer_in_use); + return apic->lapic_timer.hv_timer_in_use; +} + void kvm_lapic_switch_to_hv_timer(struct kvm_vcpu *vcpu) { struct kvm_lapic *apic = vcpu->arch.apic; WARN_ON(apic->lapic_timer.hv_timer_in_use); - if (apic_lvtt_tscdeadline(apic) && - !atomic_read(&apic->lapic_timer.pending)) { - u64 tscdeadline = apic->lapic_timer.tscdeadline; - - if (!kvm_x86_ops->set_hv_timer(vcpu, tscdeadline)) { - apic->lapic_timer.hv_timer_in_use = true; - hrtimer_cancel(&apic->lapic_timer.timer); - - /* In case the sw timer triggered in the window */ - if (atomic_read(&apic->lapic_timer.pending)) - cancel_hv_tscdeadline(apic); - } - trace_kvm_hv_timer_state(vcpu->vcpu_id, - apic->lapic_timer.hv_timer_in_use); - } + if (apic_lvtt_tscdeadline(apic)) + start_hv_tscdeadline(apic); } EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_hv_timer); @@ -1453,15 +1461,7 @@ static void start_apic_timer(struct kvm_lapic *apic) ktime_to_ns(ktime_add_ns(now, apic->lapic_timer.period))); } else if (apic_lvtt_tscdeadline(apic)) { - /* lapic timer in tsc deadline mode */ - u64 tscdeadline = apic->lapic_timer.tscdeadline; - - if (kvm_x86_ops->set_hv_timer && - !kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) { - apic->lapic_timer.hv_timer_in_use = true; - trace_kvm_hv_timer_state(apic->vcpu->vcpu_id, - apic->lapic_timer.hv_timer_in_use); - } else + if (!(kvm_x86_ops->set_hv_timer && start_hv_tscdeadline(apic))) start_sw_tscdeadline(apic); } } -- GitLab