linux-kernel - [PATCH V3] PCI: pciehp: Disable ACS Source Validation during hot-remove

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Message-ID: <20230730191519.3124390-1-vidyas@nvidia.com>
Date:   Mon, 31 Jul 2023 00:45:19 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     <bhelgaas@...gle.com>, <lukas@...ner.de>,
        <alex.williamson@...hat.com>, <treding@...dia.com>,
        <jonathanh@...dia.com>
CC:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <vsethi@...dia.com>, <kthota@...dia.com>, <mmaddireddy@...dia.com>,
        <vidyas@...dia.com>, <sagar.tv@...il.com>
Subject: [PATCH V3] PCI: pciehp: Disable ACS Source Validation during hot-remove

PCIe 6.0, 6.12.1.1 specifies that downstream devices are permitted to
send upstream messages before they have been assigned a bus number and
such messages have a Requester ID with Bus number set to 00h.
If the Downstream port has ACS Source Validation enabled, these messages
will be detected as ACS violation error.

Hence, disable ACS Source Validation in the bridge device during
hot-remove operation and re-enable it after enumeration of the
downstream hierarchy but before binding the respective device drivers.

Signed-off-by: Vidya Sagar <vidyas@...dia.com>
---
v3:
* Addressed review comments from Bjon

v2:
* Fixed build issues

 drivers/pci/hotplug/pciehp_pci.c | 13 ++++++++++++-
 drivers/pci/pci.c                | 21 +++++++++++++++++++++
 include/linux/pci.h              |  6 ++++++
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
index ad12515a4a12..42d4328f2a9b 100644
--- a/drivers/pci/hotplug/pciehp_pci.c
+++ b/drivers/pci/hotplug/pciehp_pci.c
@@ -63,6 +63,7 @@ int pciehp_configure_device(struct controller *ctrl)
 
 	pci_assign_unassigned_bridge_resources(bridge);
 	pcie_bus_configure_settings(parent);
+	pci_configure_acs_sv(bridge, true);
 
 	/*
 	 * Release reset_lock during driver binding
@@ -132,6 +133,16 @@ void pciehp_unconfigure_device(struct controller *ctrl, bool presence)
 		}
 		pci_dev_put(dev);
 	}
-
+	/*
+	 * PCIe 6.0, 6.12.1.1 specifies that downstream devices are permitted
+	 * to send upstream messages before they have been assigned a bus
+	 * number and such messages have a Requester ID with Bus number
+	 * set to 00h. If the Downstream port has ACS Source Validation enabled,
+	 * these messages will be detected as ACS violation error.
+	 * Hence, disable ACS Source Validation here and re-enable it after
+	 * enumeration of the downstream hierarchy and before binding the
+	 * respective device drivers in pciehp_configure_device().
+	 */
+	pci_configure_acs_sv(ctrl->pcie->port, false);
 	pci_unlock_rescan_remove();
 }
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 60230da957e0..5a21640de355 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1004,6 +1004,27 @@ static void pci_enable_acs(struct pci_dev *dev)
 	pci_disable_acs_redir(dev);
 }
 
+#ifdef CONFIG_HOTPLUG_PCI_PCIE
+void pci_configure_acs_sv(struct pci_dev *dev, bool flag)
+{
+	u16 cap;
+	u16 ctrl;
+
+	if (!pci_acs_enable || !dev->acs_cap)
+		return;
+
+	pci_read_config_word(dev, dev->acs_cap + PCI_ACS_CAP, &cap);
+	pci_read_config_word(dev, dev->acs_cap + PCI_ACS_CTRL, &ctrl);
+
+	if (flag)
+		ctrl |= (cap & PCI_ACS_SV);
+	else
+		ctrl &= ~(cap & PCI_ACS_SV);
+
+	pci_write_config_word(dev, dev->acs_cap + PCI_ACS_CTRL, ctrl);
+}
+#endif
+
 /**
  * pci_restore_bars - restore a device's BAR values (e.g. after wake-up)
  * @dev: PCI device to have its BARs restored
diff --git a/include/linux/pci.h b/include/linux/pci.h
index eeb2e6f6130f..b6d53fe28371 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -2350,6 +2350,12 @@ void pci_hp_create_module_link(struct pci_slot *pci_slot);
 void pci_hp_remove_module_link(struct pci_slot *pci_slot);
 #endif
 
+#ifdef CONFIG_HOTPLUG_PCI_PCIE
+void pci_configure_acs_sv(struct pci_dev *dev, bool flag);
+#else
+static inline void pci_configure_acs_sv(struct pci_dev *dev, bool flag) { }
+#endif
+
 /**
  * pci_pcie_cap - get the saved PCIe capability offset
  * @dev: PCI device
-- 
2.25.1