[PATCH v4 5/5] iommu/amd: Fail probe on ATS configuration failure

[Pranjal Shrivastava <praan@google.com>]

Update the AMD IOMMU driver to handle ATS configuration and enablement
more strictly. Specifically, update the device probe to fail if
pci_prepare_ats() returns an error. This ensures that any ATS-capable
master reaching the attach phase is guaranteed to have a valid config.

Additionally, update pdev_enable_cap_ats() to WARN_ON() if pci_enable_ats
fails. Since earlier checks in the probe phase preclude config-related
failures, any failure during hardware enablement is considered a kernel
bug.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/iommu/amd/iommu.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 84cad43dc188..1dddb08e7b22 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -570,10 +570,16 @@ static inline int pdev_enable_cap_ats(struct pci_dev *pdev)
 	if (amd_iommu_iotlb_sup &&
 	    (dev_data->flags & AMD_IOMMU_DEVICE_FLAG_ATS_SUP)) {
 		ret = pci_enable_ats(pdev, PAGE_SHIFT);
-		if (!ret) {
-			dev_data->ats_enabled = 1;
-			dev_data->ats_qdep    = pci_ats_queue_depth(pdev);
-		}
+		/*
+		 * pci_enable_ats() should not fail here because earlier checks
+		 * have already verified support and configuration.
+		 */
+		if (WARN_ON(ret))
+			return ret;
+
+		dev_data->ats_enabled = 1;
+		dev_data->ats_qdep    = pci_ats_queue_depth(pdev);
+		ret = 0;
 	}
 
 	return ret;
@@ -2502,8 +2508,17 @@ static struct iommu_device *amd_iommu_probe_device(struct device *dev)
 	else
 		dev_data->max_irqs = MAX_IRQS_PER_TABLE_512;
 
-	if (dev_is_pci(dev))
-		pci_prepare_ats(to_pci_dev(dev), PAGE_SHIFT);
+	if (dev_is_pci(dev)) {
+		struct pci_dev *pdev = to_pci_dev(dev);
+
+		if (pci_ats_supported(pdev)) {
+			ret = pci_prepare_ats(pdev, PAGE_SHIFT);
+			if (ret) {
+				iommu_dev = ERR_PTR(ret);
+				goto out_err;
+			}
+		}
+	}
 
 out_err:
 	return iommu_dev;
-- 
2.54.0.746.g67dd491aae-goog