linux-kernel - [PATCH v5] PCI: hotplug: Drop checking of PCI_BRIDGE_CONTROL in *_unconfigure

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Message-Id: <20171109111508.47678-1-mika.westerberg@linux.intel.com>
Date:   Thu,  9 Nov 2017 14:15:08 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Ashok Raj <ashok.raj@...el.com>,
        Keith Busch <keith.busch@...el.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Lukas Wunner <lukas@...ner.de>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <yehezkel.bernat@...el.com>,
        Mario.Limonciello@...l.com,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v5] PCI: hotplug: Drop checking of PCI_BRIDGE_CONTROL in *_unconfigure_device()

During PCIe surprise hot-unplug the device is not accessible anymore and
register reads return 0xffffffff. When that happens pciehp_unconfigure_device()
may inadvertently think the device below the bridge may be a display
device of somesort as reading PCI_BRIDGE_CONTROL register also returns
0xff. This results failure of the remove operation:

  pciehp 0000:00:1c.0:pcie004: Slot(0): Link Down
  pciehp 0000:00:1c.0:pcie004: Slot(0): Card present
  pciehp 0000:00:1c.0:pcie004: Cannot remove display device 0000:01:00.0

Because of this the hierarchy is left untouched preventing further
hotplug operations.

Now, it is not clear why the check is there in the first place and why
we would like to prevent removing a bridge if it has PCI_BRIDGE_CTL_VGA
set. In case of PCIe surprise hot-unplug, it would not even be possible
to prevent the removal.

Given this and the issue described above, I think it makes sense to drop
the whole PCI_BRIDGE_CONTROL check from pciehp_unconfigure_device().
While there do the same for shpchp_configure_device() based on the same
reasoning and the fact that the same bug might trigger in standard PCI
hotplug as well.

Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
---
The previous version (v4) of the patch can be found here:

  https://patchwork.kernel.org/patch/10026551/

Changes from v4:

  - Drop the check from shpchp_configure_device() as well

 drivers/pci/hotplug/pciehp_pci.c | 12 ------------
 drivers/pci/hotplug/shpchp_pci.c | 12 ------------
 2 files changed, 24 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
index 2a1ca020cf5a..acc360d1a1fb 100644
--- a/drivers/pci/hotplug/pciehp_pci.c
+++ b/drivers/pci/hotplug/pciehp_pci.c
@@ -79,7 +79,6 @@ int pciehp_configure_device(struct slot *p_slot)
 int pciehp_unconfigure_device(struct slot *p_slot)
 {
 	int rc = 0;
-	u8 bctl = 0;
 	u8 presence = 0;
 	struct pci_dev *dev, *temp;
 	struct pci_bus *parent = p_slot->ctrl->pcie->port->subordinate;
@@ -101,17 +100,6 @@ int pciehp_unconfigure_device(struct slot *p_slot)
 	list_for_each_entry_safe_reverse(dev, temp, &parent->devices,
 					 bus_list) {
 		pci_dev_get(dev);
-		if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE && presence) {
-			pci_read_config_byte(dev, PCI_BRIDGE_CONTROL, &bctl);
-			if (bctl & PCI_BRIDGE_CTL_VGA) {
-				ctrl_err(ctrl,
-					 "Cannot remove display device %s\n",
-					 pci_name(dev));
-				pci_dev_put(dev);
-				rc = -EINVAL;
-				break;
-			}
-		}
 		if (!presence) {
 			pci_dev_set_disconnected(dev, NULL);
 			if (pci_has_subordinate(dev))
diff --git a/drivers/pci/hotplug/shpchp_pci.c b/drivers/pci/hotplug/shpchp_pci.c
index ea63db58b4b1..79f1682c858e 100644
--- a/drivers/pci/hotplug/shpchp_pci.c
+++ b/drivers/pci/hotplug/shpchp_pci.c
@@ -78,7 +78,6 @@ int shpchp_configure_device(struct slot *p_slot)
 int shpchp_unconfigure_device(struct slot *p_slot)
 {
 	int rc = 0;
-	u8 bctl = 0;
 	struct pci_bus *parent = p_slot->ctrl->pci_dev->subordinate;
 	struct pci_dev *dev, *temp;
 	struct controller *ctrl = p_slot->ctrl;
@@ -93,17 +92,6 @@ int shpchp_unconfigure_device(struct slot *p_slot)
 			continue;
 
 		pci_dev_get(dev);
-		if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE) {
-			pci_read_config_byte(dev, PCI_BRIDGE_CONTROL, &bctl);
-			if (bctl & PCI_BRIDGE_CTL_VGA) {
-				ctrl_err(ctrl,
-					 "Cannot remove display device %s\n",
-					 pci_name(dev));
-				pci_dev_put(dev);
-				rc = -EINVAL;
-				break;
-			}
-		}
 		pci_stop_and_remove_bus_device(dev);
 		pci_dev_put(dev);
 	}
-- 
2.14.2