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From:   Andy Lutomirski <luto@kernel.org>
Date:   Wed, 19 Feb 2020 09:21:48 -0800
Message-ID: <CALCETrWBEDjenqze3wVc6TkUt_g+OFx9TQbYysLH+6fku=aWjQ@mail.gmail.com>
Subject: Re: [PATCH v3 02/22] x86,mce: Delete ist_begin_non_atomic()
To:     Borislav Petkov <bp@alien8.de>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Greg KH <gregkh@linuxfoundation.org>, gustavo@embeddedor.com,
        Thomas Gleixner <tglx@linutronix.de>, paulmck@kernel.org,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Andrew Lutomirski <luto@kernel.org>,
        Tony Luck <tony.luck@intel.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Masami Hiramatsu <mhiramat@kernel.org>
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On Wed, Feb 19, 2020 at 9:13 AM Borislav Petkov <bp@alien8.de> wrote:
>
> On Wed, Feb 19, 2020 at 03:47:26PM +0100, Peter Zijlstra wrote:
> > Subject: Re: [PATCH v3 02/22] x86,mce: Delete ist_begin_non_atomic()
>
> x86/mce: ...
>
> > It is an abomination; and in prepration of removing the whole
> > ist_enter() thing, it needs to go.
> >
> > Convert #MC over to using task_work_add() instead; it will run the
> > same code slightly later, on the return to user path of the same
> > exception.
>
> That's fine because the error happened in userspace.

Unless there is a signal pending and the signal setup code is about to
hit the same failed memory.  I suppose we can just treat cases like
this as "oh well, time to kill the whole system".

But we should genuinely agree that we're okay with deferring this handling.