PCI: Allow all bus devices to use the same slot

A PCIe hotplug slot applies to the entire secondary bus. Thus, pciehp only
allocates a single hotplug_slot for the bridge to that bus. The existing
PCI slot, though, would only match to functions on device 0, meaning any
devices beyond that, e.g., ARI functions, are not matched to any slot even
though they share it. A slot reset will break all the missing devices
because the handling skips them.

For example, ARI devices with more than 8 functions fail because their
state is not properly handled, nor is the attached driver notified of the
reset. In the best case, the device will appear unresponsive to the driver,
resulting in unexpected errors. A worse possibility may panic the kernel if
in-flight transactions trigger hardware reported errors like this real
observation:

  vfio-pci 0000:01:00.0: resetting
  vfio-pci 0000:01:00.0: reset done
  {1}[Hardware Error]:  Error 1, type: fatal
  {1}[Hardware Error]:   section_type: PCIe error
  {1}[Hardware Error]:   port_type: 0, PCIe end point
  {1}[Hardware Error]:   version: 0.2
  {1}[Hardware Error]:   command: 0x0140, status: 0x0010
  {1}[Hardware Error]:   device_id: 0000:01:01.0
  {1}[Hardware Error]:   slot: 0
  {1}[Hardware Error]:   secondary_bus: 0x00
  {1}[Hardware Error]:   vendor_id: 0x1d9b, device_id: 0x0207
  {1}[Hardware Error]:   class_code: 020000
  {1}[Hardware Error]:   bridge: secondary_status: 0x0000, control: 0x0000
  {1}[Hardware Error]:   aer_cor_status: 0x00008000, aer_cor_mask: 0x00002000
  {1}[Hardware Error]:   aer_uncor_status: 0x00010000, aer_uncor_mask: 0x00100000
  {1}[Hardware Error]:   aer_uncor_severity: 0x006f6030
  {1}[Hardware Error]:   TLP Header: 0a412800 00192080 60000004 00000004
  GHES: Fatal hardware error but panic disabled
  Kernel panic - not syncing: GHES: Fatal hardware error

Allow a slot to be created to claim all devices on a bus, not just a
matching device. This is done by introducing a sentinel value, named
PCI_SLOT_ALL_DEVICES, which then has the PCI slot match to any device on
the bus. This fixes slot resets for pciehp.

Since 0xff already has special meaning, the chosen value for this new
feature is 0xfe. This will not clash with any actual slot number since they
are limited to 5 bits.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://patch.msgid.link/20260217160836.2709885-3-kbusch@meta.com

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