[PATCH] KVM: nVMX: Fix exception injection

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

 WARNING: CPU: 3 PID: 2840 at arch/x86/kvm/vmx.c:10966 nested_vmx_vmexit+0xdcd/0xde0 [kvm_intel]
 CPU: 3 PID: 2840 Comm: qemu-system-x86 Tainted: G           OE   4.12.0-rc3+ #23
 RIP: 0010:nested_vmx_vmexit+0xdcd/0xde0 [kvm_intel]
 Call Trace:
  ? kvm_check_async_pf_completion+0xef/0x120 [kvm]
  ? rcu_read_lock_sched_held+0x79/0x80
  vmx_queue_exception+0x104/0x160 [kvm_intel]
  ? vmx_queue_exception+0x104/0x160 [kvm_intel]
  kvm_arch_vcpu_ioctl_run+0x1171/0x1ce0 [kvm]
  ? kvm_arch_vcpu_load+0x47/0x240 [kvm]
  ? kvm_arch_vcpu_load+0x62/0x240 [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+0x81/0x220
  entry_SYSCALL64_slow_path+0x25/0x25

This is triggered occasionally by running both win7 and win2016 in L2, in 
addition, EPT is disabled on both L1 and L2. It can't be reproduced easily.

Commit 0b6ac343fc (KVM: nVMX: Correct handling of exception injection) mentioned 
that "KVM wants to inject page-faults which it got to the guest. This function 
assumes it is called with the exit reason in vmcs02 being a #PF exception". 
Commit e011c663 (KVM: nVMX: Check all exceptions for intercept during delivery to 
L2) allows to check all exceptions for intercept during delivery to L2. However, 
there is no guarantee the exit reason is exception currently, when there is an 
external interrupt occurred on host, maybe a time interrupt for host which should 
not be injected to guest, and somewhere queues an exception, then the function 
nested_vmx_check_exception() will be called and the vmexit emulation codes will 
try to emulate the "Acknowledge interrupt on exit" behavior, the warning is 
triggered.

This patch fixes it by confirming to inject exception to the guest when the exit 
reason in vmcs02 is exception. 

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9b4b5d6..778a8f3 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2422,7 +2422,8 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned nr)
 {
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 
-	if (!(vmcs12->exception_bitmap & (1u << nr)))
+	if (to_vmx(vcpu)->exit_reason != EXIT_REASON_EXCEPTION_NMI ||
+		!(vmcs12->exception_bitmap & (1u << nr)))
 		return 0;
 
 	nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason,
-- 
2.7.4