Re: [PATCH V6] Introduce a new flag for i440fx to disable PCI hotplug on the root bus

[Igor Mammedov]

On Fri, 21 Aug 2020 11:16:12 +0200
Igor Mammedov <imammedo@redhat.com> wrote:

> On Thu, 20 Aug 2020 22:11:41 +0530
> Ani Sinha <ani@anisinha.ca> wrote:
> 
> > > On Aug 20, 2020, at 9:11 PM, Ani Sinha <ani@anisinha.ca> wrote:
> > > 
> > > On Thu, Aug 20, 2020 at 7:37 PM Igor Mammedov <imammedo@redhat.com> 
> > > wrote:    
> > >>     
> > >>> On Thu, 20 Aug 2020 14:51:56 +0530
> > >>> Ani Sinha <ani@anisinha.ca> wrote:
> > >>> 
> > >>> We introduce a new global flag 'acpi-root-pci-hotplug' for i440fx with 
> > >>> which
> > >>> we can turn on or off PCI device hotplug on the root bus. This flag can 
> > >>> be
> > >>> used to prevent all PCI devices from getting hotplugged or unplugged 
> > >>> from the
> > >>> root PCI bus.
> > >>> This feature is targetted mostly towards Windows VMs. It is useful in 
> > >>> cases
> > >>> where some hypervisor admins want to deploy guest VMs in a way so that 
> > >>> the
> > >>> users of the guest OSes are not able to hot-eject certain PCI devices 
> > >>> from
> > >>> the Windows system tray. Laine has explained the use case here in 
> > >>> detail:
> > >>> https://www.redhat.com/archives/libvir-list/2020-February/msg00110.html
> > >>> 
> > >>> Julia has resolved this issue for PCIE buses with the following commit:
> > >>> 530a0963184e57e71a5b538 ("pcie_root_port: Add hotplug disabling option")
> > >>> 
> > >>> This commit attempts to introduce similar behavior for PCI root buses 
> > >>> used in
> > >>> i440fx machine types (although in this case, we do not have a per-slot
> > >>> capability to turn hotplug on or off).
> > >>> 
> > >>> Usage:
> > >>>   -global PIIX4_PM.acpi-root-pci-hotplug=off
> > >>> 
> > >>> By default, this option is enabled which means that hotplug is turned 
> > >>> on for
> > >>> the PCI root bus.
> > >>> 
> > >>> The previously existing flag 'acpi-pci-hotplug-with-bridge-support' for 
> > >>> PCI-PCI
> > >>> bridges remain as is and can be used along with this new flag to 
> > >>> control PCI
> > >>> hotplug on PCI bridges.
> > >>> 
> > >>> This change has been tested using a Windows 2012R2 server guest image 
> > >>> and also
> > >>> with a Windows 2019 server guest image on a Ubuntu 18.04 host using the 
> > >>> latest
> > >>> master qemu from upstream (v5.1.0 tag).
> > >>> 
> > >>> Signed-off-by: Ani Sinha <ani@anisinha.ca>
> > >>> ---
> > >>> hw/acpi/piix4.c      |  8 ++++++--
> > >>> hw/i386/acpi-build.c | 26 +++++++++++++++++++-------
> > >>> 2 files changed, 25 insertions(+), 9 deletions(-)
> > >>> 
> > >>> Change Log:
> > >>> V5..V6: specified upstream master tag information off which this patch 
> > >>> is
> > >>> based off of.
> > >>> 
> > >>> diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
> > >>> index 26bac4f16c..4f436e5bf3 100644
> > >>> --- a/hw/acpi/piix4.c
> > >>> +++ b/hw/acpi/piix4.c
> > >>> @@ -78,6 +78,7 @@ typedef struct PIIX4PMState {
> > >>> 
> > >>>     AcpiPciHpState acpi_pci_hotplug;
> > >>>     bool use_acpi_hotplug_bridge;
> > >>> +    bool use_acpi_root_pci_hotplug;
> > >>> 
> > >>>     uint8_t disable_s3;
> > >>>     uint8_t disable_s4;    
> > >>     
> > >>> @@ -595,8 +596,9 @@ static void 
> > >>> piix4_acpi_system_hot_add_init(MemoryRegion *parent,
> > >>>                           "acpi-gpe0", GPE_LEN);
> > >>>     memory_region_add_subregion(parent, GPE_BASE, &s->io_gpe);
> > >>> 
> > >>> -    acpi_pcihp_init(OBJECT(s), &s->acpi_pci_hotplug, bus, parent,
> > >>> -                    s->use_acpi_hotplug_bridge);
> > >>> +    if (s->use_acpi_hotplug_bridge || s->use_acpi_root_pci_hotplug)
> > >>> +        acpi_pcihp_init(OBJECT(s), &s->acpi_pci_hotplug, bus, parent,
> > >>> +                        s->use_acpi_hotplug_bridge);    
> > >> If intent was to disable hardware part of ACPI hotplug,
> > >> then this hunk is not enough. I'd say it introduces bug since you are 
> > >> leaving
> > >> device_add/del route open and "_E01" AML code around trying to access no 
> > >> longer
> > >> described/present io ports.
> > >> 
> > >> Without this hunk patch is fine, as a means to hide hotplug from Windows.
> > >> 
> > >> If you'd like to disable hw part, you will need to consider case where 
> > >> hotplug is
> > >> disabled completly and block all related AML and block device_add|del.
> > >> So it would be a bit more than above hunk.    
> > > 
> > > Ok maybe I will just remove it.

That's what I'd do, so that mostly AML part will be merged first and
then work on properly disabling hw parts as a separate patch.

Also Julia might borrow "acpi-root-pci-hotplug" for here q35 work.

> > >     
> > >> 
> > >>     
> > >>>     s->cpu_hotplug_legacy = true;
> > >>>     object_property_add_bool(OBJECT(s), "cpu-hotplug-legacy",
> > >>> @@ -635,6 +637,8 @@ static Property piix4_pm_properties[] = {
> > >>>     DEFINE_PROP_UINT8(ACPI_PM_PROP_S4_VAL, PIIX4PMState, s4_val, 2),
> > >>>     DEFINE_PROP_BOOL("acpi-pci-hotplug-with-bridge-support", 
> > >>> PIIX4PMState,
> > >>>                      use_acpi_hotplug_bridge, true),
> > >>> +    DEFINE_PROP_BOOL("acpi-root-pci-hotplug", PIIX4PMState,
> > >>> +                     use_acpi_root_pci_hotplug, true),
> > >>>     DEFINE_PROP_BOOL("memory-hotplug-support", PIIX4PMState,
> > >>>                      acpi_memory_hotplug.is_enabled, true),
> > >>>     DEFINE_PROP_END_OF_LIST(),
> > >>> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > >>> index b7bcbbbb2a..19a1702ad1 100644
> > >>> --- a/hw/i386/acpi-build.c
> > >>> +++ b/hw/i386/acpi-build.c
> > >>> @@ -95,6 +95,7 @@ typedef struct AcpiPmInfo {
> > >>>     bool s3_disabled;
> > >>>     bool s4_disabled;
> > >>>     bool pcihp_bridge_en;
> > >>> +    bool pcihp_root_en;
> > >>>     uint8_t s4_val;
> > >>>     AcpiFadtData fadt;
> > >>>     uint16_t cpu_hp_io_base;
> > >>> @@ -245,6 +246,9 @@ static void acpi_get_pm_info(MachineState *machine, 
> > >>> AcpiPmInfo *pm)
> > >>>     pm->pcihp_bridge_en =
> > >>>         object_property_get_bool(obj, 
> > >>> "acpi-pci-hotplug-with-bridge-support",
> > >>>                                  NULL);
> > >>> +    pm->pcihp_root_en =
> > >>> +        object_property_get_bool(obj, "acpi-root-pci-hotplug", NULL);
> > >>> +
> > >>> }
> > >>> 

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