Re: [PATCH] Add a new PIIX option to control PCI hot unplugging of devices on non-root buses - Philippe Mathieu-Daudé

From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: "Daniel P. Berrangé" <berrange@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>
Cc: Ani Sinha <ani.sinha@nutanix.com>,
	Eduardo Habkost <ehabkost@redhat.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Marcel Apfelbaum <marcel@redhat.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH] Add a new PIIX option to control PCI hot unplugging of devices on non-root buses
Date: Mon, 20 Apr 2020 13:40:24 +0200	[thread overview]
Message-ID: <5182c28e-0a84-8141-89ca-954dacfc0ca7@redhat.com> (raw)
In-Reply-To: <20200420092459.GF346737@redhat.com>

On 4/20/20 11:24 AM, Daniel P. Berrangé wrote:
> On Fri, Apr 17, 2020 at 12:09:00PM -0400, Michael S. Tsirkin wrote:
>> On Fri, Apr 17, 2020 at 03:36:14PM +0000, Ani Sinha wrote:
>>>
>>>
>>>> On Apr 17, 2020, at 8:57 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>
>>>> Is there a real reason to do this? Can't we just limit the
>>>> hotplug control to pcie ports? At some point I'd like us to
>>>> start leaving piix alone..
>>>
>>> Yes we really need this feature as want to be able to hot plug devices into the guest but prevent customers from hot unplugging them from say Windows system tray.
>>>
>>> ani
>>
>> Problem is, I think this is not something we can support with pcie or shpc.
>> I'm reluctant to add features that only ACPI can support,
>> we are trying to phase that out.
> 
>  From the upstream POV, there's been no decision / agreement to phase
> out PIIX, this is purely a RHEL downstream decision & plan. If other
> distros / users have a different POV, and find the feature useful, we
> should accept the patch if it meets the normal QEMU patch requirements.

Remotely related, this thread suggest to rename the current Frankenstein 
PIIX as 'virt_southbridge' /s
https://www.mail-archive.com/qemu-devel@nongnu.org/msg691232.html

Seriously, apparently thinking to modify PIIX scares various people.
Is there a virt equivalent that could work?
On one hand people want to use Windows guest unmodified (or with 
digitally signed drivers, which seems impossible to do with virtio 
package [*]). OTOH we are not sure how the PIIX model works because it 
is not based on specs, and does not match its datasheet, and do not want 
to modify it.

[*] If you click on 'How to Release-Sign File System Drivers' on
https://www.linux-kvm.org/page/WindowsGuestDrivers/Download_Drivers
it opens https://www.microsoft.com/whdc/driver/tips/IFS_Signing.mspx
and displays "Your request has been blocked."...

> 
> Regards,
> Daniel
> 