linux-kernel - [PATCH RFC v1 2/2] pci: Suspend ATS before doing FLR

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Message-ID: <29cc1268dfdae2a836dbdeaa4eea3bedae564497.1749494161.git.nicolinc@nvidia.com>
Date: Mon, 9 Jun 2025 11:45:14 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: <jgg@...dia.com>, <joro@...tes.org>, <will@...nel.org>,
	<robin.murphy@....com>, <bhelgaas@...gle.com>
CC: <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<linux-pci@...r.kernel.org>, <patches@...ts.linux.dev>,
	<pjaroszynski@...dia.com>, <vsethi@...dia.com>
Subject: [PATCH RFC v1 2/2] pci: Suspend ATS before doing FLR

Per PCIe r6.3, sec 10.3.1 IMPLEMENTATION NOTE, software should disable ATS
before initiating a Function Level Reset.

Call iommu_dev_reset_prepare() before FLR and iommu_dev_reset_done() after,
in the two FLR Functions. This will dock the device at IOMMU_DOMAIN_BLOCKED
during the FLR function, which should allow the IOMMU driver to pause DMA
traffic and invode pci_disable_ats() and pci_enable_ats() respectively.

Add a warning if ATS isn't disabled, in which case IOMMU driver should fix
itself to disable ATS following the design in iommu_dev_reset_prepare().

Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 drivers/pci/pci.c | 42 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e9448d55113b..61535435bde1 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -13,6 +13,7 @@
 #include <linux/delay.h>
 #include <linux/dmi.h>
 #include <linux/init.h>
+#include <linux/iommu.h>
 #include <linux/msi.h>
 #include <linux/of.h>
 #include <linux/pci.h>
@@ -4518,13 +4519,26 @@ EXPORT_SYMBOL(pci_wait_for_pending_transaction);
  */
 int pcie_flr(struct pci_dev *dev)
 {
+	int ret = 0;
+
 	if (!pci_wait_for_pending_transaction(dev))
 		pci_err(dev, "timed out waiting for pending transaction; performing function level reset anyway\n");
 
+	/*
+	 * Per PCIe r6.3, sec 10.3.1 IMPLEMENTATION NOTE, software disables ATS
+	 * before initiating a Function Level Reset. So notify the iommu driver
+	 * that actually enabled ATS. Have to call it after waiting for pending
+	 * DMA transaction.
+	 */
+	if (iommu_dev_reset_prepare(&dev->dev))
+		pci_err(dev, "failed to stop IOMMU\n");
+	if (dev->ats_enabled)
+		pci_err(dev, "failed to stop ATS\n");
+
 	pcie_capability_set_word(dev, PCI_EXP_DEVCTL, PCI_EXP_DEVCTL_BCR_FLR);
 
 	if (dev->imm_ready)
-		return 0;
+		goto done;
 
 	/*
 	 * Per PCIe r4.0, sec 6.6.2, a device must complete an FLR within
@@ -4533,7 +4547,11 @@ int pcie_flr(struct pci_dev *dev)
 	 */
 	msleep(100);
 
-	return pci_dev_wait(dev, "FLR", PCIE_RESET_READY_POLL_MS);
+	ret = pci_dev_wait(dev, "FLR", PCIE_RESET_READY_POLL_MS);
+
+done:
+	iommu_dev_reset_done(&dev->dev);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(pcie_flr);
 
@@ -4561,6 +4579,7 @@ EXPORT_SYMBOL_GPL(pcie_reset_flr);
 
 static int pci_af_flr(struct pci_dev *dev, bool probe)
 {
+	int ret = 0;
 	int pos;
 	u8 cap;
 
@@ -4587,10 +4606,21 @@ static int pci_af_flr(struct pci_dev *dev, bool probe)
 				 PCI_AF_STATUS_TP << 8))
 		pci_err(dev, "timed out waiting for pending transaction; performing AF function level reset anyway\n");
 
+	/*
+	 * Per PCIe r6.3, sec 10.3.1 IMPLEMENTATION NOTE, software disables ATS
+	 * before initiating a Function Level Reset. So notify the iommu driver
+	 * that actually enabled ATS. Have to call it after waiting for pending
+	 * DMA transaction.
+	 */
+	if (iommu_dev_reset_prepare(&dev->dev))
+		pci_err(dev, "failed to stop IOMMU\n");
+	if (dev->ats_enabled)
+		pci_err(dev, "failed to stop ATS\n");
+
 	pci_write_config_byte(dev, pos + PCI_AF_CTRL, PCI_AF_CTRL_FLR);
 
 	if (dev->imm_ready)
-		return 0;
+		goto done;
 
 	/*
 	 * Per Advanced Capabilities for Conventional PCI ECN, 13 April 2006,
@@ -4600,7 +4630,11 @@ static int pci_af_flr(struct pci_dev *dev, bool probe)
 	 */
 	msleep(100);
 
-	return pci_dev_wait(dev, "AF_FLR", PCIE_RESET_READY_POLL_MS);
+	ret = pci_dev_wait(dev, "AF_FLR", PCIE_RESET_READY_POLL_MS);
+
+done:
+	iommu_dev_reset_done(&dev->dev);
+	return ret;
 }
 
 /**
-- 
2.43.0