On Thu, Feb 03, 2022 at 11:47:09AM +0100, Blazej Kucman wrote:
> > > On Wed, Feb 02, 2022 at 04:48:01PM +0100, Blazej Kucman wrote:
> > >> On Fri, 28 Jan 2022 08:03:28 -0600
> > >> Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > >>>> On Fri, Jan 28, 2022 at 9:08 PM Bjorn Helgaas
> > >>>> <helgaas@xxxxxxxxxx> wrote:
> > >>>>> 04b12ef163d1 ("PCI: vmd: Honor ACPI _OSC on PCIe features")
> > >>>>> looks like a it could be related. Try reverting that commit
> > >>>>> and see whether it makes a difference.
> > >>>>
> > >>>> The affected NVMe is indeed behind VMD domain, so I think the
> > >>>> commit can make a difference.
> > >>>>
> > >>>> Does VMD behave differently on laptops and servers?
> > >>>> Anyway, I agree that the issue really lies in "pci=nommconf".
> > >>>
> > >>> Oh, I have a guess:
> > >>>
> > >>> - With "pci=nommconf", prior to v5.17-rc1, pciehp did not work
> > >>> in general, but *did* work for NVMe behind a VMD. As of
> > >>> v5.17-rc1, pciehp no longer works for NVMe behind VMD.
> > >>>
> > >>> - Without "pci=nommconf", pciehp works as expected for all
> > >>> devices including NVMe behind VMD, both before and after
> > >>> v5.17-rc1.
> > >>>
> > >>> Is that what you're observing?
> > >>>
> > >>> If so, I doubt there's anything to fix other than getting rid of
> > >>> "pci=nommconf".
> > >>
> > >> I haven't tested with VMD disabled earlier. I verified it and my
> > >> observations are as follows:
> > >>
> > >> OS: RHEL 8.4
> > >> NO - hotplug not working
> > >> YES - hotplug working
> > >>
> > >> pci=nommconf added:
> > >> +--------------+-------------------+---------------------+--------------+
> > >> | | pci-v5.17-changes | revert-04b12ef163d1 | inbox
> > >> kernel
> > >> +--------------+-------------------+---------------------+--------------+
> > >> | VMD enabled | NO | YES | YES
> > >> +--------------+-------------------+---------------------+--------------+
> > >> | VMD disabled | NO | NO | NO
> > >> +--------------+-------------------+---------------------+--------------+
OK, so the only possible problem case is that booting with VMD enabled
and "pci=nommconf". In that case, hotplug for devices below VMD
worked before 04b12ef163d1 and doesn't work after.
Your table doesn't show it, but hotplug for devices *not* behind VMD
should not work either before or after 04b12ef163d1 because Linux
doesn't request PCIe hotplug control when booting with "pci=nommconf".
Why were you testing with "pci=nommconf"? Do you think anybody uses
that with VMD and NVMe?
Bjorn
