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

[Marcel Apfelbaum <marcel.apfelbaum@gmail.com>]

Hi Ani,

On 4/18/20 6:25 AM, Ani Sinha wrote:
> +Julia who implemented https://patchwork.kernel.org/patch/11388881/
>
>
>> On Apr 18, 2020, at 3:26 AM, Laine Stump <laine@redhat.com> wrote:
>>
>> On 4/17/20 12:35 PM, Ani Sinha wrote:
>>> +Laine
>>>> On Apr 17, 2020, at 9:39 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>
>>>> 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.
>>> Hmm. I see. We use conventional PCI and hence was looking for providing this feature for conventional PCI only. Laine might be able to throw some lights as to feasibility of the in PCIE world.
>> Sorry, my knowledge doesn't go that low. If there's a qemu option I can expose it in libvirt, but am by no means an expert of qemu internals or the pci/pcie specs :-)
>>
>> (BTW, I think in the past people have prevented enabling hot-unplug by unprivileged users in Windows with some sort of a "system policy" in Windows. (whatever that is - I don't use Windows, and have just heard this from others when discussing the problem).
>>

A PCIe Root Port or a PCI slot can or cannot support hot-plugging. 
Anything in the middle can't be done at PCIe/PCI level (as far as I know).
I think the answer can be at the modelling level. Use non hot-pluggable 
slots (or PCIe Root Ports without hot-plug support) for the devices
you don't want hot-unplugged, leave an empty PCI Bridge (or some PCIe 
Root Ports with hot-plug support) to be able to hot-plug devices.

Thanks,
Marcel

> My question to Julia is whether it is possible to disable just hot unplug but keep hot plugging for PCIE devices enabled using PCI_EXP_SLTCAP_HPC  or otherwise in Qemu?
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>