On Fri, 11 Sep 2020 23:37:50 +0530
Ani Sinha <a...@anisinha.ca> 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 can cause devices
> attached to
> the root bus to get hot-unplugged if the user issues the following set of
> commmands:
>
> outl 0xae10 0
> outl 0xae08 your_slot
>
> Thanks to Julia for pointing this out here:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg734548.html
>
> In this patch, we fix the issue in this function by checking if the bus which
> is
> returned by the function is actually hotpluggable. If not, we simply return
> NULL.
> This avoids the scenario where we were returning a non-hotpluggable bus.
>
> This patch is based off of tag v5.10
I'd put this type of comment below --- or in cover letter
so it won't be committed into git history
> Signed-off-by: Ani Sinha <a...@anisinha.ca>
Reviewed-by: Igor Mammedov <imamm...@redhat.com>
> ---
> hw/acpi/pcihp.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
> index 39b1f74442..32ae8b2c0a 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 (find.bus && !qbus_is_hotpluggable(BUS(find.bus))) {
> + find.bus = NULL;
> + }
> return find.bus;
> }
>
