linux-kernel - Re: [PATCH v2 07/11] KVM: x86: Trace re-injected exceptions

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Date:   Thu, 28 Apr 2022 12:48:39 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Maciej S . Szmigiero" <maciej.szmigiero@...cle.com>
Subject: Re: [PATCH v2 07/11] KVM: x86: Trace re-injected exceptions

On Sat, 2022-04-23 at 02:14 +0000, Sean Christopherson wrote:
> Trace exceptions that are re-injected, not just those that KVM is
> injecting for the first time.  Debugging re-injection bugs is painful
> enough as is, not having visibility into what KVM is doing only makes
> things worse.
> 
> Delay propagating pending=>injected in the non-reinjection path so that
> the tracing can properly identify reinjected exceptions.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/trace.h | 12 ++++++++----
>  arch/x86/kvm/x86.c   | 16 +++++++++-------
>  2 files changed, 17 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index de4762517569..d07428e660e3 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -358,25 +358,29 @@ TRACE_EVENT(kvm_inj_virq,
>   * Tracepoint for kvm interrupt injection:
>   */
>  TRACE_EVENT(kvm_inj_exception,
> -	TP_PROTO(unsigned exception, bool has_error, unsigned error_code),
> -	TP_ARGS(exception, has_error, error_code),
> +	TP_PROTO(unsigned exception, bool has_error, unsigned error_code,
> +		 bool reinjected),
> +	TP_ARGS(exception, has_error, error_code, reinjected),
>  
>  	TP_STRUCT__entry(
>  		__field(	u8,	exception	)
>  		__field(	u8,	has_error	)
>  		__field(	u32,	error_code	)
> +		__field(	bool,	reinjected	)
>  	),
>  
>  	TP_fast_assign(
>  		__entry->exception	= exception;
>  		__entry->has_error	= has_error;
>  		__entry->error_code	= error_code;
> +		__entry->reinjected	= reinjected;
>  	),
>  
> -	TP_printk("%s (0x%x)",
> +	TP_printk("%s (0x%x)%s",
>  		  __print_symbolic(__entry->exception, kvm_trace_sym_exc),
>  		  /* FIXME: don't print error_code if not present */
> -		  __entry->has_error ? __entry->error_code : 0)
> +		  __entry->has_error ? __entry->error_code : 0,
> +		  __entry->reinjected ? " [reinjected]" : "")
>  );
>  
>  /*
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 951d0a78ccda..c3ee8dc00d3a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9393,6 +9393,11 @@ int kvm_check_nested_events(struct kvm_vcpu *vcpu)
>  
>  static void kvm_inject_exception(struct kvm_vcpu *vcpu)
>  {
> +	trace_kvm_inj_exception(vcpu->arch.exception.nr,
> +				vcpu->arch.exception.has_error_code,
> +				vcpu->arch.exception.error_code,
> +				vcpu->arch.exception.injected);
> +
>  	if (vcpu->arch.exception.error_code && !is_protmode(vcpu))
>  		vcpu->arch.exception.error_code = false;
>  	static_call(kvm_x86_queue_exception)(vcpu);
> @@ -9450,13 +9455,6 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool *req_immediate_exit)
>  
>  	/* try to inject new event if pending */
>  	if (vcpu->arch.exception.pending) {
> -		trace_kvm_inj_exception(vcpu->arch.exception.nr,
> -					vcpu->arch.exception.has_error_code,
> -					vcpu->arch.exception.error_code);
> -
> -		vcpu->arch.exception.pending = false;
> -		vcpu->arch.exception.injected = true;
> -
>  		if (exception_type(vcpu->arch.exception.nr) == EXCPT_FAULT)
>  			__kvm_set_rflags(vcpu, kvm_get_rflags(vcpu) |
>  					     X86_EFLAGS_RF);
> @@ -9470,6 +9468,10 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool *req_immediate_exit)
>  		}
>  
>  		kvm_inject_exception(vcpu);
> +
> +		vcpu->arch.exception.pending = false;
> +		vcpu->arch.exception.injected = true;
> +
>  		can_inject = false;
>  	}
>  

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky