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

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Message-ID: <YoyRo6gJrr4lsFpD@alley>
Date:   Tue, 24 May 2022 10:04:51 +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>,
        Desmond yan <desmond.yan@...adcom.com>,
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Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list

On Mon 2022-05-23 11:56:12, Guilherme G. Piccoli wrote:
> On 19/05/2022 16:20, Scott Branden wrote:
> > [...] 
> >> Hi Scott / Desmond, thanks for the detailed answer! Is this adapter
> >> designed to run in x86 only or you have other architectures' use cases?
> > The adapter may be used in any PCIe design that supports DMA.
> > So it may be possible to run in arm64 servers.
> >>
> >> [...]
> >> With that said, and given this is a lightweight notifier that ideally
> >> should run ASAP, I'd keep this one in the hypervisor list. We can
> >> "adjust" the semantic of this list to include lightweight notifiers that
> >> reset adapters.
> > Sounds the best to keep system operating as tested today.
> >>
> >> With that said, Petr has a point - not always such list is going to be
> >> called before kdump. So, that makes me think in another idea: what if we
> >> have another list, but not on panic path, but instead in the custom
> >> crash_shutdown()? Drivers could add callbacks there that must execute
> >> before kexec/kdump, no matter what.
> > It may be beneficial for some other drivers but for our use we would 
> > then need to register for the panic path and the crash_shutdown path. 
> > We notify the VK card for 2 purposes: one to stop DMA so memory stop 
> > changing during a kdump.  And also to get the card into a good state so 
> > resets happen cleanly.
> 
> Thanks Scott! With that, I guess it's really better to keep this
> notifier in this hypervisor/early list - I'm planning to do that for V2.
> Unless Petr or somebody has strong feelings against that, of course.

I am fine with it because we do not have a better solution at the
moment.

It might be a good candidate for the 5th notifier list mentioned
in the thread https://lore.kernel.org/r/YoyQyHHfhIIXSX0U@alley .
But I am not sure if the 5th list is worth the complexity.

Best Regards,
Petr