From: Wanpeng Li Date: Sun, 21 May 2017 03:32:32 +0000 (-0700) Subject: KVM: X86: Fix preempt the preemption timer cancel X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=5acc1ca4fb15f00bfa3d4046e35ca381bc25d580;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git KVM: X86: Fix preempt the preemption timer cancel Preemption can occur during cancel preemption timer, and there will be inconsistent status in lapic, vmx and vmcs field. CPU0 CPU1 preemption timer vmexit handle_preemption_timer(vCPU0) kvm_lapic_expired_hv_timer vmx_cancel_hv_timer vmx->hv_deadline_tsc = -1 vmcs_clear_bits /* hv_timer_in_use still true */ sched_out sched_in kvm_arch_vcpu_load vmx_set_hv_timer write vmx->hv_deadline_tsc vmcs_set_bits /* back in kvm_lapic_expired_hv_timer */ hv_timer_in_use = false ... vmx_vcpu_run vmx_arm_hv_run write preemption timer deadline spurious preemption timer vmexit handle_preemption_timer(vCPU0) kvm_lapic_expired_hv_timer WARN_ON(!apic->lapic_timer.hv_timer_in_use); This can be reproduced sporadically during boot of L2 on a preemptible L1, causing a splat on L1. WARNING: CPU: 3 PID: 1952 at arch/x86/kvm/lapic.c:1529 kvm_lapic_expired_hv_timer+0xb5/0xd0 [kvm] CPU: 3 PID: 1952 Comm: qemu-system-x86 Not tainted 4.12.0-rc1+ #24 RIP: 0010:kvm_lapic_expired_hv_timer+0xb5/0xd0 [kvm] Call Trace: handle_preemption_timer+0xe/0x20 [kvm_intel] vmx_handle_exit+0xc9/0x15f0 [kvm_intel] ? lock_acquire+0xdb/0x250 ? lock_acquire+0xdb/0x250 ? kvm_arch_vcpu_ioctl_run+0xdf3/0x1ce0 [kvm] kvm_arch_vcpu_ioctl_run+0xe55/0x1ce0 [kvm] kvm_vcpu_ioctl+0x384/0x7b0 [kvm] ? kvm_vcpu_ioctl+0x384/0x7b0 [kvm] ? __fget+0xf3/0x210 do_vfs_ioctl+0xa4/0x700 ? __fget+0x114/0x210 SyS_ioctl+0x79/0x90 do_syscall_64+0x8f/0x750 ? trace_hardirqs_on_thunk+0x1a/0x1c entry_SYSCALL64_slow_path+0x25/0x25 This patch fixes it by disabling preemption while cancelling preemption timer. This way cancel_hv_timer is atomic with respect to kvm_arch_vcpu_load. Cc: Paolo Bonzini Cc: Radim Krčmář Signed-off-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index c329d2894905..6e6f345adfe6 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1495,8 +1495,10 @@ EXPORT_SYMBOL_GPL(kvm_lapic_hv_timer_in_use); static void cancel_hv_timer(struct kvm_lapic *apic) { + 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)