Re: [PATCH] Introduce global piix flag to disable PCI hotplug

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Aug 10, 2020 at 08:24:53PM +0530, Ani Sinha wrote:
> 
> 
> On Mon, Aug 10, 2020 at 8:17 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> 
>     On Mon, Aug 10, 2020 at 04:59:41PM +0530, Ani Sinha wrote:
>     > We introduce a new global flag for PIIX with which we can
>     > turn on or off PCI device hotplug. This flag can be used
>     > to prevent all PCI devices from getting hotplugged/unplugged
>     > on the PCI bus. The new options disables all hotpluh HW
>     > initialization code as well as the ACPI AMLs.
>     >
>     > Signed-off-by: Ani Sinha <ani@anisinha.ca>
> 
>     Well we have a flag like this for pci bridges, right?
>     So all that's left is an option to disable hotplug
>     for the pci root, right?
>     Wouldn't that be better than disabling it globally?
> 
> 
> The idea is to have just one option to disable all hotplug globally. But if you
> want to have two flags one for the bridges and one for the pci root, we can
> certainly look into it.
> 

I can certainly see the attraction of a global flag.

However, with the interface we have for bridges right now, how are we
going to resolve the conflict if hotplug is disabled globally but
enabled for a given bridge?

A reasonable way would be to change the default value for bridges,
have a user-specified value override it.
This patch doesn't do it, though.




> 
> 
>     > ---
>     >  hw/acpi/piix4.c      |  8 ++++++--
>     >  hw/i386/acpi-build.c | 20 ++++++++++++++------
>     >  2 files changed, 20 insertions(+), 8 deletions(-)
>     >
>     > diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
>     > index 26bac4f..8b13e86 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_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_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-pci-hotplug", PIIX4PMState,
>     > +                     use_acpi_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 b7bcbbb..343b9b6 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_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_en =
>     > +        object_property_get_bool(obj, "acpi-pci-hotplug", NULL);
>     > +
>     >  }
>     > 
>     >  static void acpi_get_misc_info(AcpiMiscInfo *info)
>     > @@ -337,14 +341,16 @@ 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_en)
>     >  {
>     >      Aml *dev, *notify_method = NULL, *method;
>     > -    QObject *bsel;
>     > +    QObject *bsel = NULL;
>     >      PCIBus *sec;
>     >      int i;
>     > 
>     > -    bsel = object_property_get_qobject(OBJECT(bus),
>     ACPI_PCIHP_PROP_BSEL, NULL);
>     > +    if (pcihp_en)
>     > +        bsel = object_property_get_qobject(OBJECT(bus),
>     > +                                           ACPI_PCIHP_PROP_BSEL, NULL);
>     >      if (bsel) {
>     >          uint64_t bsel_val = qnum_get_uint(qobject_to(QNum, bsel));
>     > 
>     > @@ -439,7 +445,8 @@ 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_en);
>     >          }
>     >          /* slot descriptor has been composed, add it into parent context
>     */
>     >          aml_append(parent_scope, dev);
>     > @@ -468,7 +475,7 @@ static void build_append_pci_bus_devices(Aml
>     *parent_scope, PCIBus *bus,
>     >      }
>     > 
>     >      /* Notify about child bus events in any case */
>     > -    if (pcihp_bridge_en) {
>     > +    if (pcihp_bridge_en && pcihp_en) {
>     >          QLIST_FOREACH(sec, &bus->child, sibling) {
>     >              int32_t devfn = sec->parent_dev->devfn;
>     > 
>     > @@ -1818,7 +1825,8 @@ 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_en);
>     > 
>     >              if (TPM_IS_TIS_ISA(tpm)) {
>     >                  if (misc->tpm_version == TPM_VERSION_2_0) {
>     > --
>     > 2.7.4
> 
>