On Sat, Aug 29, 2020 at 01:42:33PM +0530, Ani Sinha wrote:
> When ACPI hotplug for the root bus is disabled, the bsel property for that
> bus is not set. Please see the following commit:
>
> 3d7e78aa7777f ("Introduce a new flag for i440fx to disable PCI hotplug on the
> root bus").
>
> As a result, when acpi_pcihp_find_hotplug_bus() is called
> with bsel set to 0, it may return the root bus. This would be wrong since the
> root bus is not hotpluggable. In general, this can potentially happen to other
> buses as well.
> In this patch, we fix the issue in this function by checking if the bus
> returned
> by the function is actually hotpluggable. If not, we simply return NULL. This
> avoids the scenario where we are actually returning a non-hotpluggable bus.
>
> Signed-off-by: Ani Sinha <a...@anisinha.ca>
What exactly are the consequences though?
> ---
> hw/acpi/pcihp.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
> index 39b1f74442..f148e73c89 100644
> --- a/hw/acpi/pcihp.c
> +++ b/hw/acpi/pcihp.c
> @@ -147,6 +147,21 @@ static PCIBus
> *acpi_pcihp_find_hotplug_bus(AcpiPciHpState *s, int bsel)
> if (!bsel && !find.bus) {
> find.bus = s->root;
> }
> +
> + /*
> + * Check if find.bus is actually hotpluggable. If bsel is set to
> + * NULL for example on the root bus in order to make it
> + * non-hotpluggable, find.bus will match the root bus when bsel
> + * is 0. See acpi_pcihp_test_hotplug_bus() above. Since the
> + * bus is not hotpluggable however, we should not select the bus.
> + * Instead, we should set find.bus to NULL in that case. In the check
> + * below, we generalize this case for all buses, not just the root bus.
> + * The callers of this function check for a null return value and
> + * handle them appropriately.
> + */
> + if (!qbus_is_hotpluggable(BUS(find.bus))) {
> + find.bus = NULL;
> + }
> return find.bus;
> }
>
> --
> 2.17.1
