linux-kernel - Re: [PATCH] pciehp: fast unplug for virtual machines

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Message-ID: <20211115095946.54tp5glmgfged3rz@sirius.home.kraxel.org>
Date:   Mon, 15 Nov 2021 10:59:46 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pciehp: fast unplug for virtual machines

  Hi,

> > This requires guest specific code though. Emulating the attention button
> > works in a guest independent way.
> 
> It sounds like you're using the Attention Button because it does
> almost, but not quite what you want for your specific use case.

Well, we want send a request to the guest to shutdown and poweroff the
device.

> Why don't you just trigger surprise-removal from outside the guest?

To give the guest a chance to shutdown the device gracefully?
Umount filesystems, flush data to disk.

Also guest stability.  Traditionally linux isn't very good at dealing
with surprise removal, although the situation is improving.

Emulating surprise-removal has been discussed too.  More as fallback
in case the guest doesn't respond to the attention button.  Right now
we don't have it but should be doable.  For some kinds of devices it
shouldn't be a problem to go straight to surprise-removal.

I'll go experiment with that.

take care,
  Gerd