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

[Ani Sinha]

On Mon, Aug 10, 2020 at 9:11 PM Ani Sinha <ani@anisinha.ca> wrote:
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> Ani
> On Aug 10, 2020, 20:49 +0530, Michael S. Tsirkin <mst@redhat.com>, wrote:
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> On Mon, Aug 10, 2020 at 08:35:56PM +0530, Ani Sinha wrote:
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> Ani
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> On Aug 10, 2020, 20:30 +0530, Michael S. Tsirkin <mst@redhat.com>, wrote:
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> On Mon, Aug 10, 2020 at 08:24:53PM +0530, Ani Sinha wrote:
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> On Mon, Aug 10, 2020 at 8:17 PM Michael S. Tsirkin <mst@redhat.com>
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> wrote:
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> On Mon, Aug 10, 2020 at 04:59:41PM +0530, Ani Sinha wrote:
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> We introduce a new global flag for PIIX with which we can
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> turn on or off PCI device hotplug. This flag can be used
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> to prevent all PCI devices from getting hotplugged/unplugged
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> on the PCI bus. The new options disables all hotpluh HW
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> initialization code as well as the ACPI AMLs.
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> Signed-off-by: Ani Sinha <ani@anisinha.ca>
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> Well we have a flag like this for pci bridges, right?
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> So all that's left is an option to disable hotplug
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> for the pci root, right?
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> Wouldn't that be better than disabling it globally?
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> The idea is to have just one option to disable all hotplug globally.
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> But if you
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> want to have two flags one for the bridges and one for the pci root, we
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> can
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> certainly look into it.
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> I can certainly see the attraction of a global flag.
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> However, with the interface we have for bridges right now, how are we
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> going to resolve the conflict if hotplug is disabled globally but
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> enabled for a given bridge?
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> A reasonable way would be to change the default value for bridges,
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> have a user-specified value override it.
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> This patch doesn't do it, though.
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> I think the global option should override the bridge option. So if the global
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> option disables hotplug, the bridge option should be a noop.
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> Well just ignoring inconsistent user input does not sound great.
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> Tends to create support problems.
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> Then I suggest we take your original idea - have the new option just disable 
> hotplug on the pci root bus.
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> This would be cleaner and would introduce less confusion.  Also the patch 
> should be simple.

I have sent a patch to this effect.

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> ---
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> hw/acpi/piix4.c | 8 ++++++--
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> hw/i386/acpi-build.c | 20 ++++++++++++++------
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> 2 files changed, 20 insertions(+), 8 deletions(-)
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> diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
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> index 26bac4f..8b13e86 100644
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> --- a/hw/acpi/piix4.c
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> +++ b/hw/acpi/piix4.c
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> @@ -78,6 +78,7 @@ typedef struct PIIX4PMState {
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> AcpiPciHpState acpi_pci_hotplug;
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> bool use_acpi_hotplug_bridge;
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> + bool use_acpi_pci_hotplug;
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> uint8_t disable_s3;
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> uint8_t disable_s4;
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> @@ -595,8 +596,9 @@ static void piix4_acpi_system_hot_add_init
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> (MemoryRegion *parent,
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> "acpi-gpe0", GPE_LEN);
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> memory_region_add_subregion(parent, GPE_BASE, &s->io_gpe);
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> - acpi_pcihp_init(OBJECT(s), &s->acpi_pci_hotplug, bus, parent,
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> - s->use_acpi_hotplug_bridge);
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> + if (s->use_acpi_pci_hotplug)
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> + acpi_pcihp_init(OBJECT(s), &s->acpi_pci_hotplug, bus,
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> parent,
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> + s->use_acpi_hotplug_bridge);
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> s->cpu_hotplug_legacy = true;
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> object_property_add_bool(OBJECT(s), "cpu-hotplug-legacy",
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> @@ -635,6 +637,8 @@ static Property piix4_pm_properties[] = {
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> DEFINE_PROP_UINT8(ACPI_PM_PROP_S4_VAL, PIIX4PMState, s4_val,
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> 2),
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> DEFINE_PROP_BOOL("acpi-pci-hotplug-with-bridge-support",
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> PIIX4PMState,
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> use_acpi_hotplug_bridge, true),
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> + DEFINE_PROP_BOOL("acpi-pci-hotplug", PIIX4PMState,
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> + use_acpi_pci_hotplug, true),
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> DEFINE_PROP_BOOL("memory-hotplug-support", PIIX4PMState,
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> acpi_memory_hotplug.is_enabled, true),
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> DEFINE_PROP_END_OF_LIST(),
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> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
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> index b7bcbbb..343b9b6 100644
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> --- a/hw/i386/acpi-build.c
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> +++ b/hw/i386/acpi-build.c
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> @@ -95,6 +95,7 @@ typedef struct AcpiPmInfo {
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> bool s3_disabled;
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> bool s4_disabled;
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> bool pcihp_bridge_en;
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> + bool pcihp_en;
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> uint8_t s4_val;
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> AcpiFadtData fadt;
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> uint16_t cpu_hp_io_base;
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> @@ -245,6 +246,9 @@ static void acpi_get_pm_info(MachineState
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> *machine,
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> AcpiPmInfo *pm)
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> pm->pcihp_bridge_en =
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> object_property_get_bool(obj,
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> "acpi-pci-hotplug-with-bridge-support",
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> NULL);
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> + pm->pcihp_en =
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> + object_property_get_bool(obj, "acpi-pci-hotplug", NULL);
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> +
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> }
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> static void acpi_get_misc_info(AcpiMiscInfo *info)
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> @@ -337,14 +341,16 @@ static void build_append_pcihp_notify_entry
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> (Aml
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> *method, int slot)
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> }
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> static void build_append_pci_bus_devices(Aml *parent_scope,
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> PCIBus *bus,
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> - bool pcihp_bridge_en)
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> + bool pcihp_bridge_en,
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> bool
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> pcihp_en)
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> {
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> Aml *dev, *notify_method = NULL, *method;
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> - QObject *bsel;
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> + QObject *bsel = NULL;
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> PCIBus *sec;
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> int i;
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> - bsel = object_property_get_qobject(OBJECT(bus),
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> ACPI_PCIHP_PROP_BSEL, NULL);
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> + if (pcihp_en)
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> + bsel = object_property_get_qobject(OBJECT(bus),
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> + ACPI_PCIHP_PROP_BSEL,
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> NULL);
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> if (bsel) {
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> uint64_t bsel_val = qnum_get_uint(qobject_to(QNum,
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> bsel));
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> @@ -439,7 +445,8 @@ static void build_append_pci_bus_devices(Aml
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> *parent_scope, PCIBus *bus,
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> */
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> PCIBus *sec_bus = pci_bridge_get_sec_bus(PCI_BRIDGE
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> (pdev));
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> - build_append_pci_bus_devices(dev, sec_bus,
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> pcihp_bridge_en);
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> + build_append_pci_bus_devices(dev, sec_bus,
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> pcihp_bridge_en,
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> + pcihp_en);
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> }
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> /* slot descriptor has been composed, add it into parent
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> context
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> */
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> aml_append(parent_scope, dev);
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> @@ -468,7 +475,7 @@ static void build_append_pci_bus_devices(Aml
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> *parent_scope, PCIBus *bus,
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> }
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> /* Notify about child bus events in any case */
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> - if (pcihp_bridge_en) {
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> + if (pcihp_bridge_en && pcihp_en) {
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> QLIST_FOREACH(sec, &bus->child, sibling) {
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> int32_t devfn = sec->parent_dev->devfn;
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> @@ -1818,7 +1825,8 @@ build_dsdt(GArray *table_data, BIOSLinker
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> *linker,
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> if (bus) {
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> Aml *scope = aml_scope("PCI0");
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> /* Scan all PCI buses. Generate tables to support
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> hotplug. *
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> /
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> - build_append_pci_bus_devices(scope, bus, pm->
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> pcihp_bridge_en);
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> + build_append_pci_bus_devices(scope, bus, pm->
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> pcihp_bridge_en,
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> + pm->pcihp_en);
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> if (TPM_IS_TIS_ISA(tpm)) {
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> if (misc->tpm_version == TPM_VERSION_2_0) {
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> --
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> 2.7.4
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