Re: [PATCH v3] i440fx/acpi: do not add hotplug related amls for cold plugged bridges

[Julia Suvorova]

On Fri, Sep 4, 2020 at 6:10 PM Ani Sinha <ani@anisinha.ca> wrote:
>
> Cold plugged bridges are not hot unpluggable, even when their hotplug
> property (acpi-pci-hotplug-with-bridge-support) is turned off. Please see
> the function acpi_pcihp_pc_no_hotplug() (thanks Julia). 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. This is because we add amls like _EJ0 etc for the
> pci slot where the bridge is cold plugged. 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-pluggable/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>

Reviewed-by: Julia Suvorova <jusual@redhat.com>

BTW, aren't all bridges handled in build_append_pci_bus_devices() cold-plugged?

> ---
>  hw/i386/acpi-build.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> changelog:
> v3: commit log updates providing more accurate information as received from 
> Julia.
> v2: cosmetic commit log updates with patch testing information.
> 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
>