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

[Ani Sinha]

On Fri, Sep 11, 2020 at 9:22 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> 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?

There were no unit tests to cover this bridge flag. I have added the
unit tests. It's the same one you have queued.

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