[PATCH v13 3/3] iommu/vt-d: improve ITE fault handling if target device isn't valid

[Ethan Zhao]

Because surprise removal could happen anytime, e.g. user could request safe
removal to EP(endpoint device) via sysfs and brings its link down to do
surprise removal cocurrently. such aggressive cases would cause ATS
invalidation request issued to non-existence target device, then deadly
loop to retry that request after ITE fault triggered in interrupt context.
this patch aims to optimize the ITE handling by checking the target device
presence state to avoid retrying the timeout request blindly, thus avoid
hard lockup or system hang.

Devices are valid ATS invalidation request target only when they reside
in the iommu->device_rbtre (probed, not released) and present.

Signed-off-by: Ethan Zhao <haifeng.zhao@xxxxxxxxxxxxxxx>
---
 drivers/iommu/intel/dmar.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index d14797aabb7a..d01d68205557 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1273,6 +1273,9 @@ static int qi_check_fault(struct intel_iommu *iommu, int index, int wait_index)
 {
 	u32 fault;
 	int head, tail;
+	u64 iqe_err, ite_sid;
+	struct device *dev = NULL;
+	struct pci_dev *pdev = NULL;
 	struct q_inval *qi = iommu->qi;
 	int shift = qi_shift(iommu);
 
@@ -1317,6 +1320,13 @@ static int qi_check_fault(struct intel_iommu *iommu, int index, int wait_index)
 		tail = readl(iommu->reg + DMAR_IQT_REG);
 		tail = ((tail >> shift) - 1 + QI_LENGTH) % QI_LENGTH;
 
+		/*
+		 * SID field is valid only when the ITE field is Set in FSTS_REG
+		 * see Intel VT-d spec r4.1, section 11.4.9.9
+		 */
+		iqe_err = dmar_readq(iommu->reg + DMAR_IQER_REG);
+		ite_sid = DMAR_IQER_REG_ITESID(iqe_err);
+
 		writel(DMA_FSTS_ITE, iommu->reg + DMAR_FSTS_REG);
 		pr_info("Invalidation Time-out Error (ITE) cleared\n");
 
@@ -1326,6 +1336,21 @@ static int qi_check_fault(struct intel_iommu *iommu, int index, int wait_index)
 			head = (head - 2 + QI_LENGTH) % QI_LENGTH;
 		} while (head != tail);
 
+		/*
+		 * If got ITE, we need to check if the sid of ITE is one of the
+		 * current valid ATS invalidation target devices, if no, or the
+		 * target device isn't presnet, don't try this request anymore.
+		 * 0 value of ite_sid means old VT-d device, no ite_sid value.
+		 */
+		if (ite_sid) {
+			dev = device_rbtree_find(iommu, ite_sid);
+			if (!dev || !dev_is_pci(dev))
+				return -ETIMEDOUT;
+			pdev = to_pci_dev(dev);
+			if (!pci_device_is_present(pdev) &&
+				ite_sid == pci_dev_id(pci_physfn(pdev)))
+				return -ETIMEDOUT;
+		}
 		if (qi->desc_status[wait_index] == QI_ABORT)
 			return -EAGAIN;
 	}
-- 
2.31.1