[SRU][F, J, L, M, N][PATCH 0/1] Hotplugging SCSI disk in QEMU VM fails

[Chengen Du]

Hi Tim,

Upstream has reverted two commits in a single commit, and you can find it here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5df12742b7e3aae2594a30a9d14d5d6e9e7699f4

I have directly backported this commit to address the revert of the
related commits.

Best regards,
Chengen Du

On Thu, Jan 4, 2024 at 12:54 AM Tim Gardner <tim.gardner at canonical.com> wrote:
>
> On 12/25/23 11:26 PM, Chengen Du wrote:
> > BugLink: https://bugs.launchpad.net/bugs/2047382
> >
> > SRU Justification:
> >
> > [Impact]
> > Hot-plugging SCSI disks for QEMU VMs booting with UEFI and using guest kernels >= 6.5 might be broken.
> > The inconsistency suggests a potential race condition.
> >
> > [Fix]
> > Reverting the two specified commits appears to restore reliability.
> > ==========
> > cc22522fd55e2 PCI: acpiphp: Use pci_assign_unassigned_bridge_resources() only for non-root bus
> > 40613da52b13f PCI: acpiphp: Reassign resources on bridge if necessary
> > ==========
> >
> > Upstream has resolved the issue by reverting both commits through a commit placed below.
> > ==========
> > 5df12742b7e3a Revert "PCI: acpiphp: Reassign resources on bridge if necessary
> > ==========
> >
> > [Test Plan]
> > 1. Create a VM
> > virt-install --name scsi_test --memory 2048 --vcpus 2 --boot uefi --disk path=/home/ubuntu/mantic-server-cloudimg-amd64.img,size=20,format=qcow2,bus=virtio -os-variant=ubuntu18.04 --graphics spice --network bridge=virbr0
> > 2. Prepare two XMLs for adding two disk devices
> > # cat disk_X.xml
> > <disk type='file' device='disk'>
> >    <driver name='qemu' type='raw'/>
> >    <source file='XXX.img'/>
> >    <target dev='vdX' bus='virtio'/>
> > </disk>
> > 3. Hotplug disks and check for success
> > virsh attach-device scsi_test disk_X.xml
> >
> > [Where problems could occur]
> > The patch reverts two commits that previously addressed long-standing issues related to hotplugging devices with large BARs.
> > While this reversion may reintroduce legacy issues, it does not introduce new problems.
> > The associated risks are deemed low, making it worthwhile to address timing issues during the hotplugging of SCSI disks in QEMU VM.
> >
> > Bjorn Helgaas (1):
> >    Revert "PCI: acpiphp: Reassign resources on bridge if necessary"
> >
> >   drivers/pci/hotplug/acpiphp_glue.c | 9 +++------
> >   1 file changed, 3 insertions(+), 6 deletions(-)
> >
>
> You mention reverting 2 patches, but I only see one.
> --
> -----------
> Tim Gardner
> Canonical, Inc
>