linux-kernel - Re: [PATCH] kvm/x86/vmx: report KVM_SYSTEM_EVENT

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Date:   Tue, 28 Mar 2017 03:51:01 -0400 (EDT)
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     rkrcmar@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] kvm/x86/vmx: report KVM_SYSTEM_EVENT_CRASH on triple
 fault


> While debugging a kernel issue, I found that QEMU always reboots when an
> x86 triple fault occurs, which complicates debugging.  QEMU and libvirt
> have a facility for creating a dump when KVM reports
> KVM_SYSTEM_EVENT_CRASH.  So change the VMX triple fault handler to do
> that.  This gives user space the ability to decide whether to dump,
> pause, shutdown, or reboot.

You probably want QEMU's -no-reboot option.

Triple faults are already reported to userspace with KVM_EXIT_SHUTDOWN,
and it's up to userspace to decide what to do with it.  This patch cannot
be applied, because there are guests that do a triple-fault intentionally
in order to reset the machine.

Paolo

> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  arch/x86/kvm/vmx.c         | 3 ++-
>  include/trace/events/kvm.h | 3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 3acde66..1f2694c 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5731,7 +5731,8 @@ static int handle_external_interrupt(struct kvm_vcpu
> *vcpu)
>  
>  static int handle_triple_fault(struct kvm_vcpu *vcpu)
>  {
> -	vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> +	vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
> +	vcpu->run->system_event.type = KVM_SYSTEM_EVENT_CRASH;
>  	return 0;
>  }
>  
> diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
> index 8ade3eb..200a3d7 100644
> --- a/include/trace/events/kvm.h
> +++ b/include/trace/events/kvm.h
> @@ -14,7 +14,8 @@
>  	ERSN(SHUTDOWN), ERSN(FAIL_ENTRY), ERSN(INTR), ERSN(SET_TPR),	\
>  	ERSN(TPR_ACCESS), ERSN(S390_SIEIC), ERSN(S390_RESET), ERSN(DCR),\
>  	ERSN(NMI), ERSN(INTERNAL_ERROR), ERSN(OSI), ERSN(PAPR_HCALL),	\
> -	ERSN(S390_UCONTROL), ERSN(WATCHDOG), ERSN(S390_TSCH)
> +	ERSN(S390_UCONTROL), ERSN(WATCHDOG), ERSN(S390_TSCH),		\
> +	ERSN(SYSTEM_EVENT)
>  
>  TRACE_EVENT(kvm_userspace_exit,
>  	    TP_PROTO(__u32 reason, int errno),
> --
> 2.7.4
> 
>