linux-kernel - [PATCH] KVM: X86: Fix preempt the preemption timer cancel

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Date:   Sat, 20 May 2017 20:32:32 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH] KVM: X86: Fix preempt the preemption timer cancel

From: Wanpeng Li <wanpeng.li@...mail.com>

 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 can be reproduced sporadically during boot L2 on a preemptible L1, and 
splat on L1.

          CPU0                              CPU1 

vmx_cancel_hv_timer
  vCPU0's vmx->hv_deadline_tsc = -1

  preempt occur

                                     clear preemption timer field in CPU1's active vmcs
                                     vCPU0's apic_timer.hv_timer_in_use = false
vmx_vcpu_run(vCPU0)
  vmx_arm_hv_timer
    if (vmx->hv_deadline_tsc == -1)
	  nothing change
	 
handle_preemption_timer(vCPU0)
  kvm_lapic_expired_hv_timer
    WARN_ON(!apic->lapic_timer.hv_timer_in_use); 
  
Preemption can occur during cancel preemption timer, and there will be inconsistent 
status in lapic, vmx and vmcs field. This patch fixes it by disable preemption for 
cancelling preemption timer.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 arch/x86/kvm/lapic.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index c329d28..6e6f345 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)
-- 
2.7.4