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

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 20 Aug 2020 22:11:41 +0530
Ani Sinha <ani@anisinha.ca> wrote:

> > On Aug 20, 2020, at 9:11 PM, Ani Sinha <ani@anisinha.ca> wrote:
> > 
> > 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 :(  
> 
> By that I mean the devices attached to bridges also seems to be disabled from hotplug from within Windows. I do not understand why that would be the case when the pci_bus_is_root() should be false for the secondary buses.
> 
>  Any ideas?
Looking at acpi_set_pci_info() and debugging it might help.

> 
> >   
> >> 
> >>   
> >>>         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) {  
> >>   
>