linux-kernel - Re: [patch V4 part 2 13/18] x86/kvm: Move context tracking where it belongs

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Date:   Fri, 8 May 2020 17:14:49 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <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>,
        Paolo Bonzini <pbonzini@...hat.com>,
        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 13/18] x86/kvm: Move context tracking where it belongs

On Tue, May 5, 2020 at 7:14 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Context tracking for KVM happens way too early in the vcpu_run()
> code. Anything after guest_enter_irqoff() and before guest_exit_irqoff()
> cannot use RCU and should also be not instrumented.
>
> The current way of doing this covers way too much code. Move it closer to
> the actual vmenter/exit code.

Now you've made me wonder what happens if someone traces
vmx_vcpu_run().  I'm not sure I really want to think about this.