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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [patch 1/5] tracehook: Provide TIF_NOTIFY_RESUME handling for KVM
Date:   Thu, 1 Aug 2019 10:02:38 -0700
Message-Id: <05C28F0C-5D8C-4A77-8D1B-FAC91DCF1115@amacapital.net>
References: <20190801143250.370326052@linutronix.de> <20190801143657.785902257@linutronix.de> <20190801144814.GC31398@hirez.programming.kicks-ass.net>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Ingo Molnar <mingo@kernel.org>,
        Sebastian Siewior <bigeasy@linutronix.de>,
        Anna-Maria Gleixner <anna-maria@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Julia Cartwright <julia@ni.com>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, kvm@vger.kernel.org,
        Radim Krcmar <rkrcmar@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        John Stultz <john.stultz@linaro.org>,
        Andy Lutomirski <luto@kernel.org>,
        "Paul E. McKenney" <paulmck@linux.ibm.com>
In-Reply-To: <20190801144814.GC31398@hirez.programming.kicks-ass.net>
To:     Peter Zijlstra <peterz@infradead.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Aug 1, 2019, at 7:48 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
>> On Thu, Aug 01, 2019 at 04:32:51PM +0200, Thomas Gleixner wrote:
>> +#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
>> +/**
>> + * tracehook_handle_notify_resume - Notify resume handling for virt
>> + *
>> + * Called with interrupts and preemption enabled from VMENTER/EXIT.
>> + */
>> +void tracehook_handle_notify_resume(void)
>> +{
>> +    local_irq_disable();
>> +    while (test_and_clear_thread_flag(TIF_NOTIFY_RESUME)) {
>> +        local_irq_enable();
>> +        tracehook_notify_resume(NULL);
>> +        local_irq_disable();
>> +    }
>> +    local_irq_enable();
> 
> I'm confused by the IRQ state swizzling here, what is it doing?

Me too. Also, why is a loop needed?

> 
>> +}
>> +EXPORT_SYMBOL_GPL(tracehook_handle_notify_resume);
>> +#endif
>> 
>>