linux-kernel - Re: [tip:x86/urgent] x86/mm/kmmio: Fix mmiotrace for page unaligned addresses

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Message-ID: <20171212145105.6rfbdbty6e5ajron@hirez.programming.kicks-ass.net>
Date:   Tue, 12 Dec 2017 15:51:05 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ilia Mirkin <imirkin@...m.mit.edu>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Pekka Paalanen <ppaalanen@...il.com>, Lyude <lyude@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Karol Herbst <kherbst@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, hpa@...or.com,
        linux-tip-commits@...r.kernel.org,
        Karol Herbst <karolherbst@...il.com>
Subject: Re: [tip:x86/urgent] x86/mm/kmmio: Fix mmiotrace for page unaligned
 addresses

On Tue, Dec 12, 2017 at 09:47:05AM -0500, Ilia Mirkin wrote:
> > So this 'thing' has huge gaping SMP holes in.
> 
> Sure does! Probably why the following happens when mmiotrace is enabled:
> 
> void enable_mmiotrace(void)
> {
>         mutex_lock(&mmiotrace_mutex);
>         if (is_enabled())
>                 goto out;
> 
>         if (nommiotrace)
>                 pr_info("MMIO tracing disabled.\n");
>         kmmio_init();
>         enter_uniprocessor();

	^^^^^

Ah! I completely missed that. OK, that makes it much less broken :-)

If I don't forget, I'll add some comments to this file to clarify that.

Thanks!

>         spin_lock_irq(&trace_lock);
>         atomic_inc(&mmiotrace_enabled);
>         spin_unlock_irq(&trace_lock);
>         pr_info("enabled.\n");
> out:
>         mutex_unlock(&mmiotrace_mutex);
> }