Re: [PATCH v1] i440fx/acpi: don't hot-unplug cold plugged bridges when their hotplug switch is off

[Julia Suvorova]

On Fri, Sep 4, 2020 at 10:25 AM Ani Sinha <ani@anisinha.ca> wrote:
>
> Cold plugged bridges should not be hot unpluggable, even when their hotplug 
> property
> (acpi-pci-hotplug-with-bridge-support) is turned off.

Unplugging a cold-plugged bridge is impossible already, see
acpi_pcihp_pc_no_hotplug().

Best regards, Julia Suvorova.

> 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 running on Ubuntu 
> 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(-)
>
> 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
>