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

[Marcel Apfelbaum <marcel.apfelbaum@gmail.com>]

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>
---
 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