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

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Message-ID: <da465baf0ebcfa3c31e5be7e70319b0796ac59da.camel@infradead.org>
Date:   Mon, 20 Nov 2023 12:19:51 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     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 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?

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


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