[PATCH v2] i440fx/acpi: disable hotplug of cold plugged bridges regarldless of hotplug switch

[Ani Sinha]

Cold plugged bridges should not be hot unpluggable, even when their hotplug
property (acpi-pci-hotplug-with-bridge-support) is turned off. However, with
the current implementaton, windows would try to hot-unplug a pci bridge when
it's hotplug switch is off. This is regardless of whether there are devices
attached to the bridge. When devices are attached to the bridge, the bridge
is ultimately not hot-unpluggable. We have a demo video here:
https://youtu.be/pME2sjyQweo

In this fix, we identify a cold plugged bridge and for cold plugged bridges,
we do not add the appropriate amls and acpi methods that are used by the OS
to identify a hot-unpluggable pci device. After this change, Windows does not
show an option to eject the PCI bridge. A demo video is here:
https://youtu.be/kbgej5B9Hgs

While at it, I have also updated a stale comment.

This change is tested with a Windows 2012R2 guest image and Windows 2019 server
guest image running on Ubuntu 18.04 host. This change is based off of upstream
qemu master branch tag v5.1.0.

Signed-off-by: Ani Sinha <ani@anisinha.ca>
---
 hw/i386/acpi-build.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Changelog:
v2: cosmetic commit log update.
v1: initial patch.

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index b7bcbbbb2a..90b863f4ec 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -359,6 +359,7 @@ static void build_append_pci_bus_devices(Aml *parent_scope, 
PCIBus *bus,
         int slot = PCI_SLOT(i);
         bool hotplug_enabled_dev;
         bool bridge_in_acpi;
+        bool cold_plugged_bridge;
 
         if (!pdev) {
             if (bsel) { /* add hotplug slots for non present devices */
@@ -380,15 +381,14 @@ static void build_append_pci_bus_devices(Aml 
*parent_scope, PCIBus *bus,
         pc = PCI_DEVICE_GET_CLASS(pdev);
         dc = DEVICE_GET_CLASS(pdev);
 
-        /* When hotplug for bridges is enabled, bridges are
-         * described in ACPI separately (see build_pci_bus_end).
-         * In this case they aren't themselves hot-pluggable.
+        /*
+         * Cold plugged bridges aren't themselves hot-pluggable.
          * Hotplugged bridges *are* hot-pluggable.
          */
-        bridge_in_acpi = pc->is_bridge && pcihp_bridge_en &&
-            !DEVICE(pdev)->hotplugged;
+        cold_plugged_bridge = pc->is_bridge && !DEVICE(pdev)->hotplugged;
+        bridge_in_acpi =  cold_plugged_bridge && pcihp_bridge_en;
 
-        hotplug_enabled_dev = bsel && dc->hotpluggable && !bridge_in_acpi;
+        hotplug_enabled_dev = bsel && dc->hotpluggable && !cold_plugged_bridge;
 
         if (pc->class_id == PCI_CLASS_BRIDGE_ISA) {
             continue;
-- 
2.17.1