linux-kernel - Re: [PATCH] acpi_idle: use raw_safe_halt() from acpi_idle_play

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Date:   Mon, 20 Nov 2023 13:57:46 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-acpi <linux-acpi@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, Juergen Gross <jgross@...e.com>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH] acpi_idle: use raw_safe_halt() from acpi_idle_play_dead()

On Mon, Nov 20, 2023 at 1:20 PM David Woodhouse <dwmw2@...radead.org> wrote:
>
> On Fri, 2023-10-27 at 21:14 +0200, Peter Zijlstra wrote:
> > On Fri, Oct 27, 2023 at 07:36:51PM +0100, David Woodhouse wrote:
> > > From: David Woodhouse <dwmw@...zon.co.uk>
> > >
> > > Xen HVM guests were observed taking triple-faults when attempting to
> > > online a previously offlined vCPU.
> > >
> > > Investigation showed that the fault was coming from a failing call
> > > to lockdep_assert_irqs_disabled(), in load_current_idt() which was
> > > too early in the CPU bringup to actually catch the exception and
> > > report the failure cleanly.
> > >
> > > This was a false positive, caused by acpi_idle_play_dead() setting
> > > the per-cpu hardirqs_enabled flag by calling safe_halt(). Switch it
> > > to use raw_safe_halt() instead, which doesn't do so.
> > >
> > > Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> > > ---
> > > We might {also,instead} explicitly set the hardirqs_enabled flag to
> > > zero when bringing up an AP?
> >
> > So I fixed up the idle paths the other day (see all that __cpuidle
> > stuff) but I've not yet gone through the whole hotplug thing :/
> >
> > This seems right, at this point everything, including RCU is very much
> > gone, any instrumentation is undesired.
> >
> > Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>
> Ping? Who's taking this?

I'm going to apply it.

> Needs a Cc:stable@...r.kernel.org now too, to fix 6.6.x.

Sure.