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

[Michael S. Tsirkin]

On Thu, Sep 10, 2020 at 12:19:19AM +0530, Ani Sinha wrote:
> On Sep 10, 2020, 00:00 +0530, Ani Sinha <ani@anisinha.ca>, wrote:
> 
>     On Sep 9, 2020, 23:20 +0530, Julia Suvorova <jusual@redhat.com>, wrote:
> 
>         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?
> 
> 
> 
>     Yes they are.
> 
> 
> Maybe as an improvement we can simply identify a bridge instead of a cold
> plugged bridge. However let’s have that improvement as a separate patch on top
> of this. Also let’s see what Igor thinks.

Well this changes acpi tables so I don't see how this will pass
the unit tests. Did you test this change?


> 
> 
> 
>             ---
> 
>             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
> 
> 
> 
> 
>