From: "Michael S. Tsirkin" <mst@redhat.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Gerd Hoffmann <kraxel@redhat.com>,
linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] pciehp: fast unplug for virtual machines
Date: Sun, 14 Nov 2021 17:37:15 -0500 [thread overview]
Message-ID: <20211114173550-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20211114180604.GA23907@wunner.de>
On Sun, Nov 14, 2021 at 07:06:04PM +0100, Lukas Wunner wrote:
> On Sun, Nov 14, 2021 at 12:24:43PM -0500, Michael S. Tsirkin wrote:
> > On Sun, Nov 14, 2021 at 05:39:58PM +0100, Lukas Wunner wrote:
> > > Why does virtual hardware implement the Attention Button if it's
> > > perceived as annoying? Just amend qemu so that it doesn't advertise
> > > presence of an Attention Button to get rid of the delay. (Clear the
> > > Attention Button Present bit in the Slot Capabilities register.)
> >
> > Because we want ability to request device removal from outside the
> > guest.
>
> Please elaborate. Does "outside the guest" mean on the host?
> How do you represent the Attention Button outside the guest
> and route events through to the guest?
The usual way, using kvm ioctls.
>
> > > An Attention Button doesn't make any sense for virtual hardware
> > > except to test or debug support for it in the kernel. Just make
> > > presence of the Attention Button optional and be done with it.
> > >
> > > You'll still be able to bring down the slot in software via the
> > > "remove" attribute in sysfs.
> >
> > 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.
> Now you're trying to change its behavior in a way that deviates
> from the spec to align it with your use case.
>
> Why don't you just trigger surprise-removal from outside the guest?
>
> Thanks,
>
> Lukas
Because linux does not handle it well for all devices. Fixing that
requires fixing all drivers.
--
MST
next prev parent reply other threads:[~2021-11-14 22:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 9:02 [PATCH] pciehp: fast unplug for virtual machines Gerd Hoffmann
2021-11-11 17:00 ` Michael S. Tsirkin
2021-11-12 9:56 ` Gerd Hoffmann
2021-11-12 10:09 ` Michael S. Tsirkin
2021-11-11 21:50 ` Bjorn Helgaas
2021-11-12 11:28 ` Gerd Hoffmann
2021-11-12 0:00 ` Krzysztof Wilczyński
2021-11-14 16:39 ` Lukas Wunner
2021-11-14 17:24 ` Michael S. Tsirkin
2021-11-14 18:06 ` Lukas Wunner
2021-11-14 22:37 ` Michael S. Tsirkin [this message]
2021-11-15 9:59 ` Gerd Hoffmann
2021-11-15 7:45 ` Lukas Wunner
2021-11-15 10:09 ` Gerd Hoffmann
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