Change caf108bc ("hw/i386/acpi-build: Add ACPI PCI hot-plug methods to Q35")
selects an IO address range for acpi based PCI hotplug for q35 arbitrarily. It
starts at address 0x0cc4 and ends at 0x0cdb. At the time when the patch was
written but the final version of the patch was not yet pushed upstream, this
address range was free and did not conflict with any other IO address ranges.
However, with the following change, this address range was no
longer conflict free as in this change, the IO address range
(value of ACPI_PCIHP_SIZE) was incremented by four bytes:

b32bd763 ("pci: introduce acpi-index property for PCI device")

This can be seen from the output of QMP command 'info mtree' :

0000000000000600-0000000000000603 (prio 0, i/o): acpi-evt
0000000000000604-0000000000000605 (prio 0, i/o): acpi-cnt
0000000000000608-000000000000060b (prio 0, i/o): acpi-tmr
0000000000000620-000000000000062f (prio 0, i/o): acpi-gpe0
0000000000000630-0000000000000637 (prio 0, i/o): acpi-smi
0000000000000cc4-0000000000000cdb (prio 0, i/o): acpi-pci-hotplug
0000000000000cd8-0000000000000ce3 (prio 0, i/o): acpi-cpu-hotplug

It shows that there is a region of conflict between IO regions of acpi
pci hotplug and acpi cpu hotplug.

Unfortunately, the change caf108bc did not update the IO address range
appropriately before it was pushed upstream to accommodate the increased
length of the IO address space introduced in change b32bd763.

Due to this bug, windows guests complain 'This device cannot find
enough free resources it can use' in the device manager panel for extended
IO buses. This issue also breaks the correct functioning of pci hotplug as the
following shows that the IO space for pci hotplug has been truncated:

(qemu) info mtree -f
FlatView #0
 AS "I/O", root: io
 Root memory region: io
  0000000000000cc4-0000000000000cd7 (prio 0, i/o): acpi-pci-hotplug
  0000000000000cd8-0000000000000cf7 (prio 0, i/o): acpi-cpu-hotplug

Therefore, in this fix, we adjust the IO address range for the acpi pci
hotplug so that it does not conflict with cpu hotplug and there is no
truncation of IO spaces. The starting IO address of PCI hotplug region
has been decremented by four bytes in order to accommodate four byte
increment in the IO address space introduced by change
b32bd763 ("pci: introduce acpi-index property for PCI device")

After fixing, the following are the corrected IO ranges:

0000000000000600-0000000000000603 (prio 0, i/o): acpi-evt
0000000000000604-0000000000000605 (prio 0, i/o): acpi-cnt
0000000000000608-000000000000060b (prio 0, i/o): acpi-tmr
0000000000000620-000000000000062f (prio 0, i/o): acpi-gpe0
0000000000000630-0000000000000637 (prio 0, i/o): acpi-smi
0000000000000cc0-0000000000000cd7 (prio 0, i/o): acpi-pci-hotplug
0000000000000cd8-0000000000000ce3 (prio 0, i/o): acpi-cpu-hotplug

This change has been tested using a Windows Server 2019 guest VM. Windows
no longer complains after this change.

Fixes: caf108bc ("hw/i386/acpi-build: Add ACPI PCI hot-plug methods to Q35")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/561



Signed-off-by: Ani Sinha <ani@anisinha.ca>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Julia Suvorova <jusual@redhat.com>
Message-Id: <20210916132838.3469580-3-ani@anisinha.ca>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>