linux-kernel - Re: Does anyone actually use KEXEC

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Message-ID: <Z2UbKdmmgd/IzMoz@MiWiFi-R3L-srv>
Date: Fri, 20 Dec 2024 15:22:17 +0800
From: Baoquan He <bhe@...hat.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: David Woodhouse <dwmw2@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ming Lei <ming.lei@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: Does anyone actually use KEXEC_JUMP?

On 12/16/24 at 12:21pm, Eric W. Biederman wrote:
> David Woodhouse <dwmw2@...radead.org> writes:
> 
> > It isn't broken. I know of it being used a few million times a week.
> >
> > There are corner cases which have never worked right, like the callee
> > putting a different return address for its next invocation, on the
> > stack *above* the address it 'ret's to. Which since the first kjump
> > patch has been the first word of the page *after* the swap page (and
> > is now fixed in my tree). But fundamentally it *does* work.
> >
> > I only started messing with it because I was working on
> > relocate_kernel() and needed to write a test case for it; the fact
> > that I know of it being used in production is actually just a
> > coincidence.
> 
> Cool.  I had the sense that the original developer never got around
> to using it, so I figured I should check.
> 
> Mind if I ask what you know of it being used for?

I am also very curious about the use case and asked David in other
thread, while David didn't tell. Not sure if it's one company's
confidential information. We may want to know what it's used for to
evaluate if it's a generally useful use case, or an unintentional
testing.

> 
> I had imagined it might be a way to call firmware code preventing the
> need to code of a specific interface for each type of firmware.
> 
> Eric
> 
>