Re: [PATCH V2] Add a new PIIX option to control PCI hot unplugging of devices on non-root buses

[Michael S. Tsirkin]

On Wed, Apr 29, 2020 at 07:02:56AM +0000, Ani Sinha wrote:
> 
> 
> > On Apr 29, 2020, at 12:27 PM, Michael S. Tsirkin <address@hidden> wrote:
> > 
> > On Wed, Apr 29, 2020 at 06:54:52AM +0000, Ani Sinha wrote:
> >> 
> >> 
> >>> On Apr 29, 2020, at 12:22 PM, Michael S. Tsirkin <address@hidden> wrote:
> >>> 
> >>> On Wed, Apr 29, 2020 at 06:11:20AM +0000, Ani Sinha wrote:
> >>>> 
> >>>> 
> >>>>> On Apr 29, 2020, at 10:58 AM, Michael S. Tsirkin <address@hidden> wrote:
> >>>>> 
> >>>>> o if there's a need to disable
> >>>>> just one of these, commit log needs to do a better job documenting the
> >>>>> usecase.
> >>>> 
> >>>> The use case is simple. With this feature admins will be able to do what 
> >>>> they were forced to do from Windows driver level but now at the bus 
> >>>> level. Hence, 
> >>>> (a) They need not have access to the guest VM to change or update 
> >>>> windows driver registry settings. They can enable the same setting from 
> >>>> admin management console without any access to VM.
> >>>> (b) It is more robust. No need to mess with driver settings. Incorrect 
> >>>> settings can brick guest OS. Also no guest specific knowhow required.
> >>>> (c) It is more scalable since a single cluster wide setting can be used 
> >>>> for all VM power ons and the management plane can take care of the rest 
> >>>> automatically. No need to access individual VMs to enforce this.
> >>>> (d) I am told that the driver level solution does not persist across a 
> >>>> reboot. 
> >>>> 
> >>>> Ani
> >>> 
> >>> Looks like disabling both plug and unplug would also address these needs.
> >> 
> >> No the driver level solution does not prevent hot plugging of devices but 
> >> blocks just hot unplugging. The solution I am proposing tries to do the 
> >> same but from the bus/hypervisor level.
> > 
> > Why does the driver level solution need to prevent just hot unplugging?
> 
> Because it not fair to prevent end users from hot plugging new devices when 
> it is the (accidental?) hot unplugging of existing devices which causes 
> issues.

Accidental? So maybe what you need is actually something else then -
avoid *removing* the device when it's powered down.

> > 
> > 
> >> 
> >>> -- 
> >>> MST