On Fri, Sep 30, 2022, kernel test robot wrote:
> Greeting,
>
> FYI, we noticed the following commit (built with gcc-11):
>
> commit: 7055fb11311622852c16463b1ccaa59e7691e42e ("KVM: x86: Treat pending TRIPLE_FAULT requests as pending exceptions")
> https://git.kernel.org/cgit/virt/kvm/kvm.git queue
...
> # ==== Test Assertion Failure ====
> # x86_64/mmio_warning_test.c:117: warnings_before == warnings_after
...
> [ 100.924976][ T4704] ------------[ cut here ]------------
> [ 100.931287][ T4704] WARNING: CPU: 67 PID: 4704 at arch/x86/kvm/x86.c:9934 inject_pending_event+0x6e6/0xe00 [kvm]
> [ 101.237320][ T4704] Call Trace:
> [ 101.241522][ T4704] <TASK>
> [ 101.245343][ T4704] vcpu_enter_guest+0x61a/0x3540 [kvm]
> [ 101.271009][ T4704] vcpu_run+0xbe/0x780 [kvm]
> [ 101.282791][ T4704] kvm_arch_vcpu_ioctl_run+0x334/0x1540 [kvm]
> [ 101.289810][ T4704] kvm_vcpu_ioctl+0x455/0xb00 [kvm]
> [ 101.359680][ T4704] __x64_sys_ioctl+0x128/0x1c0
> [ 101.365052][ T4704] do_syscall_64+0x38/0xc0
> [ 101.370066][ T4704] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [ 101.376647][ T4704] RIP: 0033:0x7f2a78126547
Good ol' emulated real mode. The warning exists to assert that KVM didn't queue
a new exception while injecting events, but when emulating Real Mode due to lack
of unrestricted guest, KVM needs to emulate the actual event injection and so can
trigger triple fault.
Ideally the assertion would filter out this exact case, but rmode.vm86_active is
buried in vcpu_vmx. Easiest thing is to just exempt KVM_REQ_TRIPLE_FAULT.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index eb9d2c23fb04..1d02cc416cbc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9972,7 +9972,15 @@ static int kvm_check_and_inject_events(struct kvm_vcpu *vcpu,
kvm_x86_ops.nested_ops->has_events(vcpu))
*req_immediate_exit = true;
- WARN_ON(kvm_is_exception_pending(vcpu));
+ /*
+ * KVM should never attempt to queue a new exception while injecting an
+ * event, at this point KVM is done emulating and should only propagate
+ * the exception to the VMCS/VMCB. Exempt triple faults as VMX without
+ * unrestricted guest needs to emulate Real Mode events and queues a
+ * triple fault if injection fails (see kvm_inject_realmode_interrupt()).
+ */
+ WARN_ON_ONCE(vcpu->arch.exception.pending ||
+ vcpu->arch.exception_vmexit.pending);
return 0;
out:
