linux-kernel - Re: [patch V4 part 2 14/18] x86/kvm/vmx: Add hardirq tracing to guest enter/exit

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Message-ID: <6217b923-fc1b-29c3-cab7-04b7d2d6a0fb@redhat.com>
Date:   Wed, 6 May 2020 09:55:21 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 2 14/18] x86/kvm/vmx: Add hardirq tracing to guest
 enter/exit

On 05/05/20 15:41, Thomas Gleixner wrote:
> Add hardirq tracing to guest enter/exit functions in the same way as it
> is done in the user mode enter/exit code.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c |   25 +++++++++++++++++++++++--
>  1 file changed, 23 insertions(+), 2 deletions(-)
> 
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6604,9 +6604,19 @@ static void vmx_vcpu_run(struct kvm_vcpu
>  	x86_spec_ctrl_set_guest(vmx->spec_ctrl, 0);
>  
>  	/*
> -	 * Tell context tracking that this CPU is about to enter guest mode.
> +	 * VMENTER enables interrupts (host state), but the kernel state is
> +	 * interrupts disabled when this is invoked. Also tell RCU about
> +	 * it. This is the same logic as for exit_to_user_mode().
> +	 *
> +	 * 1) Trace interrupts on state
> +	 * 2) Prepare lockdep with RCU on
> +	 * 3) Invoke context tracking if enabled to adjust RCU state
> +	 * 4) Tell lockdep that interrupts are enabled
>  	 */
> +	trace_hardirqs_on_prepare();
> +	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
>  	guest_enter_irqoff();
> +	lockdep_hardirqs_on(CALLER_ADDR0);
>  
>  	/* L1D Flush includes CPU buffer clear to mitigate MDS */
>  	if (static_branch_unlikely(&vmx_l1d_should_flush))
> @@ -6623,9 +6633,20 @@ static void vmx_vcpu_run(struct kvm_vcpu
>  	vcpu->arch.cr2 = read_cr2();
>  
>  	/*
> -	 * Tell context tracking that this CPU is back.
> +	 * VMEXIT disables interrupts (host state), but tracing and lockdep
> +	 * have them in state 'on'. Same as enter_from_user_mode().
> +	 *
> +	 * 1) Tell lockdep that interrupts are disabled
> +	 * 2) Invoke context tracking if enabled to reactivate RCU
> +	 * 3) Trace interrupts off state
> +	 *
> +	 * This needs to be done before the below as native_read_msr()
> +	 * contains a tracepoint and x86_spec_ctrl_restore_host() calls
> +	 * into world and some more.
>  	 */
> +	lockdep_hardirqs_off(CALLER_ADDR0);
>  	guest_exit_irqoff();
> +	trace_hardirqs_off_prepare();
>  
>  	/*
>  	 * We do not use IBRS in the kernel. If this vCPU has used the
> 

Acked-by: Paolo Bonzini <pbonzini@...hat.com>