Re: [PULL 06/13] Introduce a new flag for i440fx to disable PCI hotplug on the root bus

[Ani Sinha <ani@anisinha.ca>]

On Fri, Aug 28, 2020 at 6:40 PM Julia Suvorova <jusual@redhat.com> wrote:
>
> On Fri, Aug 28, 2020 at 11:53 AM Ani Sinha <ani@anisinha.ca> wrote:
> >
> >
> > Ani
> > On Aug 28, 2020, 15:19 +0530, Igor Mammedov <imammedo@redhat.com>, wrote:
> >
> > On Thu, 27 Aug 2020 23:29:34 +0530
> >
> > Ani Sinha <ani@anisinha.ca> wrote:
> >
> >
> > On Thu, Aug 27, 2020 at 11:11 PM Igor Mammedov <imammedo@redhat.com> wrote:
> >
> >
> > On Thu, 27 Aug 2020 09:40:34 -0400
> >
> > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >
> >
> > From: Ani Sinha <ani@anisinha.ca>
> >
> >
> > 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.
> >
> >
> > Signed-off-by: Ani Sinha <ani@anisinha.ca>
> >
> > Message-Id: <20200821165403.26589-1-ani@anisinha.ca>
> >
> > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> >
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> >
> >
> >
> > Tested-by: Igor Mammedov <imammedo@redhat.com>
> >
> > Reviewed-by: Igor Mammedov <imammedo@redhat.com>
> >
> > A glitch in scripts?
> >
> > I didn't review nor tested this (v8) version
> >
> >
> > oops! I am so eager to get this done and dusted :)
> >
> > it's merged now,
> >
> >
> > Wait it merged without your review?
>
> Yeah, not only added into the pull request, but actually merged.
>
> >
> > can you add a test case for it please?
> >
> >
> > You can use test_acpi_piix4_tcg_bridge() as model.
> >
> > See header comment at the top of bios-tables-test.c
> >
> > for how to prepare and submit testcase.
> >
> >
> > Will get on it.
>
> Also, while the whole approach seems good to me, it leaves the hotplug
> registers initialized (see build_piix4_pci_hotplug()), even if both
> root and bridges hotplug are disabled. Which you can exploit by
> writing something like this to the io registers:
>
> outl 0xae10 0
> outl 0xae08 your_slot
>
> And because of these quite interesting lines the device will be
> successfully unplugged:
>
> static PCIBus *acpi_pcihp_find_hotplug_bus(AcpiPciHpState *s, int bsel)
> {
> ...
>     /* Make bsel 0 eject root bus if bsel property is not set,
>      * for compatibility with non acpi setups.
>      * TODO: really needed?
>      */
>     if (!bsel && !find.bus) {
>         find.bus = s->root;
>     }
>     return find.bus;
> }
>

I have sent a patch to address this. Please review.

> Could you please cover both issues in the follow-up patches?

Also julia, looking at the code, should we also set pm->pcihp_io_len
to 0 as well in case where bridge and pci bus 0 hotplugs are both
disabled? This is because I see:

   /* reserve PCIHP resources */
    if (pm->pcihp_io_len) {

which we do not want to do if PCI hotplug is disabled altogether?

>
> Best regards, Julia Suvorova.
>
> >
> >
> >
> > ---
> >
> > include/hw/acpi/pcihp.h | 2 +-
> >
> > hw/acpi/pcihp.c | 23 ++++++++++++++++++++++-
> >
> > hw/acpi/piix4.c | 5 ++++-
> >
> > 3 files changed, 27 insertions(+), 3 deletions(-)
> >
> >
> > diff --git a/include/hw/acpi/pcihp.h b/include/hw/acpi/pcihp.h
> >
> > index 8bc4a4c01d..02f4665767 100644
> >
> > --- a/include/hw/acpi/pcihp.h
> >
> > +++ b/include/hw/acpi/pcihp.h
> >
> > @@ -67,7 +67,7 @@ void acpi_pcihp_device_unplug_request_cb(HotplugHandler *hotplug_dev,
> >
> > Error **errp);
> >
> >
> > /* Called on reset */
> >
> > -void acpi_pcihp_reset(AcpiPciHpState *s);
> >
> > +void acpi_pcihp_reset(AcpiPciHpState *s, bool acpihp_root_off);
> >
> >
> > extern const VMStateDescription vmstate_acpi_pcihp_pci_status;
> >
> >
> > diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
> >
> > index 9e31ab2da4..39b1f74442 100644
> >
> > --- a/hw/acpi/pcihp.c
> >
> > +++ b/hw/acpi/pcihp.c
> >
> > @@ -104,6 +104,24 @@ static void acpi_set_pci_info(void)
> >
> > }
> >
> > }
> >
> >
> > +static void acpi_pcihp_disable_root_bus(void)
> >
> > +{
> >
> > + static bool root_hp_disabled;
> >
> > + PCIBus *bus;
> >
> > +
> >
> > + if (root_hp_disabled) {
> >
> > + return;
> >
> > + }
> >
> > +
> >
> > + bus = find_i440fx();
> >
> > + if (bus) {
> >
> > + /* setting the hotplug handler to NULL makes the bus non-hotpluggable */
> >
> > + qbus_set_hotplug_handler(BUS(bus), NULL);
> >
> > + }
> >
> > + root_hp_disabled = true;
> >
> > + return;
> >
> > +}
> >
> > +
> >
> > static void acpi_pcihp_test_hotplug_bus(PCIBus *bus, void *opaque)
> >
> > {
> >
> > AcpiPciHpFind *find = opaque;
> >
> > @@ -209,8 +227,11 @@ static void acpi_pcihp_update(AcpiPciHpState *s)
> >
> > }
> >
> > }
> >
> >
> > -void acpi_pcihp_reset(AcpiPciHpState *s)
> >
> > +void acpi_pcihp_reset(AcpiPciHpState *s, bool acpihp_root_off)
> >
> > {
> >
> > + if (acpihp_root_off) {
> >
> > + acpi_pcihp_disable_root_bus();
> >
> > + }
> >
> > acpi_set_pci_info();
> >
> > acpi_pcihp_update(s);
> >
> > }
> >
> > diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
> >
> > index 26bac4f16c..e6163bb6ce 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;
> >
> > @@ -324,7 +325,7 @@ static void piix4_pm_reset(DeviceState *dev)
> >
> > pci_conf[0x5B] = 0x02;
> >
> > }
> >
> > pm_io_space_update(s);
> >
> > - acpi_pcihp_reset(&s->acpi_pci_hotplug);
> >
> > + acpi_pcihp_reset(&s->acpi_pci_hotplug, !s->use_acpi_root_pci_hotplug);
> >
> > }
> >
> >
> > static void piix4_pm_powerdown_req(Notifier *n, void *opaque)
> >
> > @@ -635,6 +636,8 @@ 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(),
> >
> >
> >
> >
>