On Wed, Nov 11, 2020 at 2:35 PM Michael S. Tsirkin <
mst@redhat.com> wrote:
On Thu, Oct 22, 2020 at 02:40:26PM +0300, Marcel Apfelbaum wrote:
> From: Marcel Apfelbaum <marcel@redhat.com>
>
> During PCIe Root Port's transition from Power-Off to Power-ON (or vice-versa)
> the "Slot Control Register" has the "Power Indicator Control"
> set to "Blinking" expressing a "power transition" mode.
>
> Any hotplug operation during the "power transition" mode is not permitted
> or at least not expected by the Guest OS leading to strange failures.
>
> Detect and refuse hotplug operations in such case.
>
> Signed-off-by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Going back to this I have another question: could we get
a bit more detail on when do we get into this situation?
When does guest start blinking the indicator without us
first starting a hotplug operation?
While David has more insight on the kernel behavior during the mentioned issue,
it seems the PCI subsystem sets the Power Indicator
to "blinking" as part of the init sequence of the PCIe Root Port.
The kernel will turn it off as soon as it finishes the init sequence.
A hotplug operation during the "init" sequence will surprise the Guest OS.
I'll let David to give us more info.
Thank you,
Marcel
> ---
> hw/pci/pcie.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index 5b48bae0f6..2fe5c1473f 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -410,6 +410,7 @@ void pcie_cap_slot_pre_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> PCIDevice *hotplug_pdev = PCI_DEVICE(hotplug_dev);
> uint8_t *exp_cap = hotplug_pdev->config + hotplug_pdev->exp.exp_cap;
> uint32_t sltcap = pci_get_word(exp_cap + PCI_EXP_SLTCAP);
> + uint32_t sltctl = pci_get_word(exp_cap + PCI_EXP_SLTCTL);
>
> /* Check if hot-plug is disabled on the slot */
> if (dev->hotplugged && (sltcap & PCI_EXP_SLTCAP_HPC) == 0) {
> @@ -418,6 +419,12 @@ void pcie_cap_slot_pre_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> return;
> }
>
> + if ((sltctl & PCI_EXP_SLTCTL_PIC) == PCI_EXP_SLTCTL_PWR_IND_BLINK) {
> + error_setg(errp, "Hot-plug failed: %s is in Power Transition",
> + DEVICE(hotplug_pdev)->id);
> + return;
> + }
> +
> pcie_cap_slot_plug_common(PCI_DEVICE(hotplug_dev), dev, errp);
> }
>
> --
> 2.17.2