linux-kernel - [PATCH] drivers: pci: Clear ACS state at kexec

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Date:   Sat,  4 Jan 2020 14:51:49 -0800
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     bhelgaas@...gle.com
Cc:     mika.westerberg@...ux.intel.com, alex.williamson@...hat.com,
        logang@...tatee.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] drivers: pci: Clear ACS state at kexec

ACS bits remain sticky through kexec reset. This is not really a
problem for Linux because turning IOMMU on assumes ACS on. But,
this becomes a problem if we kexec into something other than
Linux and that does not turn ACS on always.

Reset the ACS bits to default before kexec or device remove.

Signed-off-by: Deepa Dinamani <deepa.kernel@...il.com>
---
 drivers/pci/pci-driver.c |  4 ++++
 drivers/pci/pci.c        | 39 +++++++++++++++++++++++++++------------
 drivers/pci/pci.h        |  1 +
 3 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 0454ca0e4e3f..bd8d08e50b97 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -453,6 +453,8 @@ static int pci_device_remove(struct device *dev)
 
 	/* Undo the runtime PM settings in local_pci_probe() */
 	pm_runtime_put_sync(dev);
+	/* Undo the PCI ACS settings in pci_init_capabilities() */
+	pci_disable_acs(pci_dev);
 
 	/*
 	 * If the device is still on, set the power state as "unknown",
@@ -493,6 +495,8 @@ static void pci_device_shutdown(struct device *dev)
 	 */
 	if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot))
 		pci_clear_master(pci_dev);
+	if (kexec_in_progress)
+		pci_disable_acs(pci_dev);
 }
 
 #ifdef CONFIG_PM
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index da2e59daad6f..8254617cff03 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3261,15 +3261,23 @@ static void pci_disable_acs_redir(struct pci_dev *dev)
 	pci_info(dev, "disabled ACS redirect\n");
 }
 
+
+/* Standard PCI ACS capailities
+ * Source Validation | P2P Request Redirect | P2P Completion Redirect | Upstream Forwarding
+ */
+#define PCI_STD_ACS_CAP (PCI_ACS_SV | PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF)
+
 /**
- * pci_std_enable_acs - enable ACS on devices using standard ACS capabilities
+ * pci_std_enable_disable_acs - enable/disable ACS on devices using standard
+ * ACS capabilities
  * @dev: the PCI device
  */
-static void pci_std_enable_acs(struct pci_dev *dev)
+static void pci_std_enable_disable_acs(struct pci_dev *dev, int enable)
 {
 	int pos;
 	u16 cap;
 	u16 ctrl;
+	u16 val = 0;
 
 	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
 	if (!pos)
@@ -3278,19 +3286,26 @@ static void pci_std_enable_acs(struct pci_dev *dev)
 	pci_read_config_word(dev, pos + PCI_ACS_CAP, &cap);
 	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
 
-	/* Source Validation */
-	ctrl |= (cap & PCI_ACS_SV);
+	val = (cap & PCI_STD_ACS_CAP);
 
-	/* P2P Request Redirect */
-	ctrl |= (cap & PCI_ACS_RR);
+	if (enable)
+		ctrl |= val;
+	else
+		ctrl &= ~val;
 
-	/* P2P Completion Redirect */
-	ctrl |= (cap & PCI_ACS_CR);
+	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
+}
 
-	/* Upstream Forwarding */
-	ctrl |= (cap & PCI_ACS_UF);
+/**
+ * pci_disable_acs - enable ACS if hardware support it
+ * @dev: the PCI device
+ */
+void pci_disable_acs(struct pci_dev *dev)
+{
+	if (pci_acs_enable)
+		pci_std_enable_disable_acs(dev, 0);
 
-	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
+	pci_disable_acs_redir(dev);
 }
 
 /**
@@ -3305,7 +3320,7 @@ void pci_enable_acs(struct pci_dev *dev)
 	if (!pci_dev_specific_enable_acs(dev))
 		goto disable_acs_redir;
 
-	pci_std_enable_acs(dev);
+	pci_std_enable_disable_acs(dev, 1);
 
 disable_acs_redir:
 	/*
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 6394e7746fb5..480e4de46fa8 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -526,6 +526,7 @@ static inline resource_size_t pci_resource_alignment(struct pci_dev *dev,
 }
 
 void pci_enable_acs(struct pci_dev *dev);
+void pci_disable_acs(struct pci_dev *dev);
 #ifdef CONFIG_PCI_QUIRKS
 int pci_dev_specific_acs_enabled(struct pci_dev *dev, u16 acs_flags);
 int pci_dev_specific_enable_acs(struct pci_dev *dev);
-- 
2.17.1