From 1d518c6820daf4e00d29adfba980aee05f605f0f Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Tue, 25 Jul 2017 00:43:15 -0700 Subject: [PATCH] KVM: LAPIC: Fix reentrancy issues with preempt notifiers MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Preempt can occur in the preemption timer expiration handler: CPU0 CPU1 preemption timer vmexit handle_preemption_timer(vCPU0) kvm_lapic_expired_hv_timer hv_timer_is_use == true sched_out sched_in kvm_arch_vcpu_load kvm_lapic_restart_hv_timer restart_apic_timer start_hv_timer already-expired timer or sw timer triggerd in the window start_sw_timer cancel_hv_timer /* back in kvm_lapic_expired_hv_timer */ cancel_hv_timer WARN_ON(!apic->lapic_timer.hv_timer_in_use); ==> Oops This can be reproduced if CONFIG_PREEMPT is enabled. ------------[ cut here ]------------ WARNING: CPU: 4 PID: 2972 at /home/kernel/linux/arch/x86/kvm//lapic.c:1563 kvm_lapic_expired_hv_timer+0x9e/0xb0 [kvm] CPU: 4 PID: 2972 Comm: qemu-system-x86 Tainted: G OE 4.13.0-rc2+ #16 RIP: 0010:kvm_lapic_expired_hv_timer+0x9e/0xb0 [kvm] Call Trace: handle_preemption_timer+0xe/0x20 [kvm_intel] vmx_handle_exit+0xb8/0xd70 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xdd1/0x1be0 [kvm] ? kvm_arch_vcpu_load+0x47/0x230 [kvm] ? kvm_arch_vcpu_load+0x62/0x230 [kvm] kvm_vcpu_ioctl+0x340/0x700 [kvm] ? kvm_vcpu_ioctl+0x340/0x700 [kvm] ? __fget+0xfc/0x210 do_vfs_ioctl+0xa4/0x6a0 ? __fget+0x11d/0x210 SyS_ioctl+0x79/0x90 do_syscall_64+0x81/0x220 entry_SYSCALL64_slow_path+0x25/0x25 ------------[ cut here ]------------ WARNING: CPU: 4 PID: 2972 at /home/kernel/linux/arch/x86/kvm//lapic.c:1498 cancel_hv_timer.isra.40+0x4f/0x60 [kvm] CPU: 4 PID: 2972 Comm: qemu-system-x86 Tainted: G W OE 4.13.0-rc2+ #16 RIP: 0010:cancel_hv_timer.isra.40+0x4f/0x60 [kvm] Call Trace: kvm_lapic_expired_hv_timer+0x3e/0xb0 [kvm] handle_preemption_timer+0xe/0x20 [kvm_intel] vmx_handle_exit+0xb8/0xd70 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xdd1/0x1be0 [kvm] ? kvm_arch_vcpu_load+0x47/0x230 [kvm] ? kvm_arch_vcpu_load+0x62/0x230 [kvm] kvm_vcpu_ioctl+0x340/0x700 [kvm] ? kvm_vcpu_ioctl+0x340/0x700 [kvm] ? __fget+0xfc/0x210 do_vfs_ioctl+0xa4/0x6a0 ? __fget+0x11d/0x210 SyS_ioctl+0x79/0x90 do_syscall_64+0x81/0x220 entry_SYSCALL64_slow_path+0x25/0x25 This patch fixes it by making the caller of cancel_hv_timer, start_hv_timer and start_sw_timer be in preemption-disabled regions, which trivially avoid any reentrancy issue with preempt notifier. Cc: Paolo Bonzini Cc: Radim Krčmář Signed-off-by: Wanpeng Li [Add more WARNs. - Paolo] Signed-off-by: Paolo Bonzini --- arch/x86/kvm/lapic.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 2819d4c123eb..589dcc117086 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1495,11 +1495,10 @@ EXPORT_SYMBOL_GPL(kvm_lapic_hv_timer_in_use); static void cancel_hv_timer(struct kvm_lapic *apic) { + WARN_ON(preemptible()); WARN_ON(!apic->lapic_timer.hv_timer_in_use); - preempt_disable(); kvm_x86_ops->cancel_hv_timer(apic->vcpu); apic->lapic_timer.hv_timer_in_use = false; - preempt_enable(); } static bool start_hv_timer(struct kvm_lapic *apic) @@ -1507,6 +1506,7 @@ static bool start_hv_timer(struct kvm_lapic *apic) struct kvm_timer *ktimer = &apic->lapic_timer; int r; + WARN_ON(preemptible()); if (!kvm_x86_ops->set_hv_timer) return false; @@ -1538,6 +1538,8 @@ static bool start_hv_timer(struct kvm_lapic *apic) static void start_sw_timer(struct kvm_lapic *apic) { struct kvm_timer *ktimer = &apic->lapic_timer; + + WARN_ON(preemptible()); if (apic->lapic_timer.hv_timer_in_use) cancel_hv_timer(apic); if (!apic_lvtt_period(apic) && atomic_read(&ktimer->pending)) @@ -1552,15 +1554,20 @@ static void start_sw_timer(struct kvm_lapic *apic) static void restart_apic_timer(struct kvm_lapic *apic) { + preempt_disable(); if (!start_hv_timer(apic)) start_sw_timer(apic); + preempt_enable(); } void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu) { struct kvm_lapic *apic = vcpu->arch.apic; - WARN_ON(!apic->lapic_timer.hv_timer_in_use); + preempt_disable(); + /* If the preempt notifier has already run, it also called apic_timer_expired */ + if (!apic->lapic_timer.hv_timer_in_use) + goto out; WARN_ON(swait_active(&vcpu->wq)); cancel_hv_timer(apic); apic_timer_expired(apic); @@ -1569,6 +1576,8 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu) advance_periodic_target_expiration(apic); restart_apic_timer(apic); } +out: + preempt_enable(); } EXPORT_SYMBOL_GPL(kvm_lapic_expired_hv_timer); @@ -1582,9 +1591,11 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu *vcpu) { struct kvm_lapic *apic = vcpu->arch.apic; + preempt_disable(); /* Possibly the TSC deadline timer is not enabled yet */ if (apic->lapic_timer.hv_timer_in_use) start_sw_timer(apic); + preempt_enable(); } EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_sw_timer); -- 2.39.2