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From:   Thomas Gleixner <tglx@linutronix.de>
To:     paulmck@kernel.org
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [patch V4 part 1 12/36] x86/kvm: Sanitize kvm_async_pf_task_wait()
In-Reply-To: <20200505175412.GG2869@paulmck-ThinkPad-P72>
References: <20200505131602.633487962@linutronix.de> <20200505134059.262701431@linutronix.de> <20200505175412.GG2869@paulmck-ThinkPad-P72>
Date:   Tue, 05 May 2020 23:50:33 +0200
Message-ID: <87368erqza.fsf@nanos.tec.linutronix.de>
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"Paul E. McKenney" <paulmck@kernel.org> writes:
> On Tue, May 05, 2020 at 03:16:14PM +0200, Thomas Gleixner wrote:
>> RCU is watching for:
>> 
>>   #1  The vCPU exited and current is definitely not the idle task
>> 
>>   #2a The #PF entry code on the guest went through enter_from_user_mode()
>>       which reactivates RCU
>
> I have to double-check...  The NO_HZ_FULL case transitioning to/from
> userspace is entirely non-preemptible, correct?  (After rcu_user_enter()
> and before rcu_user_exit(), respectively.)

Yes. It runs with interrupts disabled down to the actual return (sysret,
iret).

Thanks,

        tglx