linux-kernel - Re: Does anyone actually use KEXEC

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Message-ID: <87bjxbzdyq.fsf@email.froward.int.ebiederm.org>
Date: Mon, 16 Dec 2024 12:21:01 -0600
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: David Woodhouse <dwmw2@...radead.org>
Cc: "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?

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 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