linux-kernel - Re: [PATCH v3 04/22] x86/doublefault: Make memmove() notrace/NOKPROBE

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Message-ID: <20200219105513.4b0b7f29@gandalf.local.home>
Date:   Wed, 19 Feb 2020 10:55:13 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, frederic@...nel.org,
        dan.carpenter@...cle.com, mhiramat@...nel.org
Subject: Re: [PATCH v3 04/22] x86/doublefault: Make memmove()
 notrace/NOKPROBE

On Wed, 19 Feb 2020 16:40:31 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> > Hmm, for things like this, which is adding notrace because of a single
> > instance of it (although it is fine to trace in any other instance), it
> > would be nice to have a gcc helper that could call "memmove+5" which
> > would skip the tracing portion.  
> 
> Or just open-code the memmove() in do_double_fault() I suppose. I don't
> think we care about super optimized code there. It's the bloody ESPFIX
> trainwreck.

Or just create a memmove_notrace() version and use that.

-- Steve