Re: [PULL 06/13] Introduce a new flag for i440fx to disable PCI hotplug on the root bus

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 27 Aug 2020 09:40:34 -0400
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> From: Ani Sinha <ani@anisinha.ca>
> 
> 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.
> 
> Signed-off-by: Ani Sinha <ani@anisinha.ca>
> Message-Id: <20200821165403.26589-1-ani@anisinha.ca>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>


> Tested-by: Igor Mammedov <imammedo@redhat.com>
> Reviewed-by: Igor Mammedov <imammedo@redhat.com>
A glitch in scripts?
I didn't review nor tested this (v8) version

> ---
>  include/hw/acpi/pcihp.h |  2 +-
>  hw/acpi/pcihp.c         | 23 ++++++++++++++++++++++-
>  hw/acpi/piix4.c         |  5 ++++-
>  3 files changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/include/hw/acpi/pcihp.h b/include/hw/acpi/pcihp.h
> index 8bc4a4c01d..02f4665767 100644
> --- a/include/hw/acpi/pcihp.h
> +++ b/include/hw/acpi/pcihp.h
> @@ -67,7 +67,7 @@ void acpi_pcihp_device_unplug_request_cb(HotplugHandler *hotplug_dev,
>                                           Error **errp);
>  
>  /* Called on reset */
> -void acpi_pcihp_reset(AcpiPciHpState *s);
> +void acpi_pcihp_reset(AcpiPciHpState *s, bool acpihp_root_off);
>  
>  extern const VMStateDescription vmstate_acpi_pcihp_pci_status;
>  
> diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
> index 9e31ab2da4..39b1f74442 100644
> --- a/hw/acpi/pcihp.c
> +++ b/hw/acpi/pcihp.c
> @@ -104,6 +104,24 @@ static void acpi_set_pci_info(void)
>      }
>  }
>  
> +static void acpi_pcihp_disable_root_bus(void)
> +{
> +    static bool root_hp_disabled;
> +    PCIBus *bus;
> +
> +    if (root_hp_disabled) {
> +        return;
> +    }
> +
> +    bus = find_i440fx();
> +    if (bus) {
> +        /* setting the hotplug handler to NULL makes the bus non-hotpluggable */
> +        qbus_set_hotplug_handler(BUS(bus), NULL);
> +    }
> +    root_hp_disabled = true;
> +    return;
> +}
> +
>  static void acpi_pcihp_test_hotplug_bus(PCIBus *bus, void *opaque)
>  {
>      AcpiPciHpFind *find = opaque;
> @@ -209,8 +227,11 @@ static void acpi_pcihp_update(AcpiPciHpState *s)
>      }
>  }
>  
> -void acpi_pcihp_reset(AcpiPciHpState *s)
> +void acpi_pcihp_reset(AcpiPciHpState *s, bool acpihp_root_off)
>  {
> +    if (acpihp_root_off) {
> +        acpi_pcihp_disable_root_bus();
> +    }
>      acpi_set_pci_info();
>      acpi_pcihp_update(s);
>  }
> diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
> index 26bac4f16c..e6163bb6ce 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;
> @@ -324,7 +325,7 @@ static void piix4_pm_reset(DeviceState *dev)
>          pci_conf[0x5B] = 0x02;
>      }
>      pm_io_space_update(s);
> -    acpi_pcihp_reset(&s->acpi_pci_hotplug);
> +    acpi_pcihp_reset(&s->acpi_pci_hotplug, !s->use_acpi_root_pci_hotplug);
>  }
>  
>  static void piix4_pm_powerdown_req(Notifier *n, void *opaque)
> @@ -635,6 +636,8 @@ 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(),