Re: [PATCH V5] Introduce a new flag for i440fx to disable PCI hotplug on the root bus

[Philippe Mathieu-Daudé]

On 8/20/20 10:16 AM, Ani Sinha 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.

"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:
> V4..V5: Updated commit message to reflect the fact that testing was also
> performed on a Windows 2019 server guest image. Minor commit log formatting
> to make sure 80 col rule is enforced.
> 
> 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);
>  
>      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);
> +
>  }
>  
>  static void acpi_get_misc_info(AcpiMiscInfo *info)
> @@ -337,15 +341,18 @@ static void build_append_pcihp_notify_entry(Aml 
> *method, int slot)
>  }
>  
>  static void build_append_pci_bus_devices(Aml *parent_scope, PCIBus *bus,
> -                                         bool pcihp_bridge_en)
> +                                         bool pcihp_bridge_en,
> +                                         bool pcihp_root_en)
>  {
>      Aml *dev, *notify_method = NULL, *method;
>      QObject *bsel;
>      PCIBus *sec;
>      int i;
> +    bool root_bus = pci_bus_is_root(bus);
> +    bool root_pcihp_disabled = (root_bus && !pcihp_root_en);
>  
>      bsel = object_property_get_qobject(OBJECT(bus), ACPI_PCIHP_PROP_BSEL, 
> NULL);
> -    if (bsel) {
> +    if (bsel && !root_pcihp_disabled) {
>          uint64_t bsel_val = qnum_get_uint(qobject_to(QNum, bsel));
>  
>          aml_append(parent_scope, aml_name_decl("BSEL", aml_int(bsel_val)));
> @@ -361,6 +368,9 @@ static void build_append_pci_bus_devices(Aml 
> *parent_scope, PCIBus *bus,
>          bool bridge_in_acpi;
>  
>          if (!pdev) {
> +            /* skip if pci hotplug for the root bus is disabled */
> +            if (root_pcihp_disabled)
> +                continue;
>              if (bsel) { /* add hotplug slots for non present devices */
>                  dev = aml_device("S%.02X", PCI_DEVFN(slot, 0));
>                  aml_append(dev, aml_name_decl("_SUN", aml_int(slot)));
> @@ -419,7 +429,7 @@ static void build_append_pci_bus_devices(Aml 
> *parent_scope, PCIBus *bus,
>              method = aml_method("_S3D", 0, AML_NOTSERIALIZED);
>              aml_append(method, aml_return(aml_int(s3d)));
>              aml_append(dev, method);
> -        } else if (hotplug_enabled_dev) {
> +        } else if (hotplug_enabled_dev && !root_pcihp_disabled) {
>              /* add _SUN/_EJ0 to make slot hotpluggable  */
>              aml_append(dev, aml_name_decl("_SUN", aml_int(slot)));
>  
> @@ -439,13 +449,14 @@ static void build_append_pci_bus_devices(Aml 
> *parent_scope, PCIBus *bus,
>               */
>              PCIBus *sec_bus = pci_bridge_get_sec_bus(PCI_BRIDGE(pdev));
>  
> -            build_append_pci_bus_devices(dev, sec_bus, pcihp_bridge_en);
> +            build_append_pci_bus_devices(dev, sec_bus, pcihp_bridge_en,
> +                                         pcihp_root_en);
>          }
>          /* slot descriptor has been composed, add it into parent context */
>          aml_append(parent_scope, dev);
>      }
>  
> -    if (bsel) {
> +    if (bsel && !root_pcihp_disabled) {
>          aml_append(parent_scope, notify_method);
>      }
>  
> @@ -455,7 +466,7 @@ static void build_append_pci_bus_devices(Aml 
> *parent_scope, PCIBus *bus,
>      method = aml_method("PCNT", 0, AML_NOTSERIALIZED);
>  
>      /* If bus supports hotplug select it and notify about local events */
> -    if (bsel) {
> +    if (bsel && !root_pcihp_disabled) {
>          uint64_t bsel_val = qnum_get_uint(qobject_to(QNum, bsel));
>  
>          aml_append(method, aml_store(aml_int(bsel_val), aml_name("BNUM")));
> @@ -1818,7 +1829,8 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
>          if (bus) {
>              Aml *scope = aml_scope("PCI0");
>              /* Scan all PCI buses. Generate tables to support hotplug. */
> -            build_append_pci_bus_devices(scope, bus, pm->pcihp_bridge_en);
> +            build_append_pci_bus_devices(scope, bus, pm->pcihp_bridge_en,
> +                                         pm->pcihp_root_en);
>  
>              if (TPM_IS_TIS_ISA(tpm)) {
>                  if (misc->tpm_version == TPM_VERSION_2_0) {
>