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

[Julia Suvorova]

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;
}

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

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(),
>
>
>
>