Re: [PATCH V6] Introduce a new flag for i440fx to disable PCI hotplug on the root bus

[Ani Sinha]

On Thu, Aug 20, 2020 at 7:37 PM Igor Mammedov <imammedo@redhat.com> wrote:
>
> On Thu, 20 Aug 2020 14:51:56 +0530
> Ani Sinha <ani@anisinha.ca> 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 (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:
> > V5..V6: specified upstream master tag information off which this patch is
> > based off of.
> >
> > 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);
> If intent was to disable hardware part of ACPI hotplug,
> then this hunk is not enough. I'd say it introduces bug since you are leaving
> device_add/del route open and "_E01" AML code around trying to access no 
> longer
> described/present io ports.
>
> Without this hunk patch is fine, as a means to hide hotplug from Windows.
>
> If you'd like to disable hw part, you will need to consider case where 
> hotplug is
> disabled completly and block all related AML and block device_add|del.
> So it would be a bit more than above hunk.

Ok maybe I will just remove it.

>
>
> >      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) {
>
> have you considered to make bus not hotpluggable,
> which should make it not to have bsel, and hence skip this branch without
> root_pcihp_disabled?
>
> see: acpi_set_bsel()
>
>
> maybe you can drop pcihp_root_en and use bsel instead of it then.
>
> it also should block device_add/del route.

This is a good idea. Therefore, I tried this:

--- a/hw/acpi/piix4.c
+++ b/hw/acpi/piix4.c
@@ -28,6 +28,7 @@
 #include "hw/pci/pci.h"
 #include "hw/qdev-properties.h"
 #include "hw/acpi/acpi.h"
+#include "hw/pci/pci_bus.h"
 #include "sysemu/runstate.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/xen.h"
@@ -507,7 +508,9 @@ static void piix4_pm_realize(PCIDevice *dev, Error **errp)

     piix4_acpi_system_hot_add_init(pci_address_space_io(dev),
                                    pci_get_bus(dev), s);
-    qbus_set_hotplug_handler(BUS(pci_get_bus(dev)), OBJECT(s));
+    if (s->use_acpi_root_pci_hotplug ||
+        !pci_bus_is_root(pci_get_bus(dev)))
+        qbus_set_hotplug_handler(BUS(pci_get_bus(dev)), OBJECT(s));

     piix4_pm_add_propeties(s);
 }


but this does not seem to be working. I am out of ideas as to why it
wouldn't work :(

>
>
> >          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) {
>