[PATCH v9 4/4] iommu/vt-d: Fail probe on ATS configuration failure

[Pranjal Shrivastava <praan@google.com>]

Update the Intel VT-d 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 iommu_enable_pci_ats() to WARN() 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.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/iommu/intel/iommu.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 849d06dfe1ae..f39451323553 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -876,8 +876,14 @@ static void iommu_enable_pci_ats(struct device_domain_info *info)
 	if (!pci_ats_page_aligned(pdev))
 		return;
 
-	if (!pci_enable_ats(pdev, VTD_PAGE_SHIFT))
-		info->ats_enabled = 1;
+	/*
+	 * pci_enable_ats() should not fail here because earlier checks
+	 * have already verified support and configuration.
+	 */
+	if (WARN_ON(pci_enable_ats(pdev, VTD_PAGE_SHIFT)))
+		return;
+
+	info->ats_enabled = 1;
 }
 
 static void iommu_disable_pci_ats(struct device_domain_info *info)
@@ -3292,7 +3298,10 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev)
 
 	dev_iommu_priv_set(dev, info);
 	if (pdev && pci_ats_supported(pdev)) {
-		pci_prepare_ats(pdev, VTD_PAGE_SHIFT);
+		ret = pci_prepare_ats(pdev, VTD_PAGE_SHIFT);
+		if (ret)
+			goto free;
+
 		ret = device_rbtree_insert(iommu, info);
 		if (ret)
 			goto free;
-- 
2.54.0.1136.gdb2ca164c4-goog