linux-kernel - Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list

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Date:   Wed, 18 May 2022 09:38:52 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     Scott Branden <scott.branden@...adcom.com>,
        Sebastian Reichel <sre@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
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Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list

On Tue 2022-05-17 13:42:06, Guilherme G. Piccoli wrote:
> On 17/05/2022 10:57, Petr Mladek wrote:
> >> Disagree here, I'm CCing Florian for information.
> >>
> >> This notifier preserves RAM so it's *very interesting* if we have
> >> kmsg_dump() for example, but maybe might be also relevant in case kdump
> >> kernel is configured to store something in a persistent RAM (then,
> >> without this notifier, after kdump reboots the system data would be lost).
> > 
> > I see. It is actually similar problem as with
> > drivers/firmware/google/gsmi.c.
> > 
> > I does similar things like kmsg_dump() so it should be called in
> > the same location (after info notifier list and before kdump).
> > 
> > A solution might be to put it at these notifiers at the very
> > end of the "info" list or make extra "dump" notifier list.
> 
> Here I still disagree. I've commented in the other response thread
> (about Google gsmi) about the semantics of the hypervisor list, but
> again: this list should contain callbacks that
> 
> (a) Should run early, _by default_ before a kdump;
> (b) Communicate with the firmware/hypervisor in a "low-risk" way;
> 
> Imagine a scenario where users configure kdump kernel to save something
> in a persistent form in DRAM - it'd be like a late pstore, in the next
> kernel. This callback enables that, it's meant to inform FW "hey, panic
> happened, please from now on don't clear the RAM in the next FW-reboot".
> I don't see a reason to postpone that - let's see if the maintainers
> have an opinion.

I have answered this in more detail in the other reply, see
https://lore.kernel.org/r/YoShZVYNAdvvjb7z@alley

I agree that both notifiers in

    drivers/soc/bcm/brcmstb/pm/pm-arm.c
    drivers/firmware/google/gsmi.c

better fit into the hypervisor list after all.

Best Regards,
Petr