Re: [PATCH] pci: Refuse to hotplug PCI Devices when the Guest OS is not ready

[Michael S. Tsirkin]

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?

> ---
>  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