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

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

On Mon, Aug 10, 2020 at 08:35:56PM +0530, Ani Sinha wrote:
> 
> Ani
> On Aug 10, 2020, 20:30 +0530, Michael S. Tsirkin <mst@redhat.com>, wrote:
> 
>     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.
> 
> 
> I think the global option should override the bridge option. So if the global
> option disables hotplug, the bridge option should be a noop.
> 

Well just ignoring inconsistent user input does not sound great.
Tends to create support problems.

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