[PATCH v11 5/5] iommu/vt-d: improve ITE fault handling if target device isn't present

[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.

Signed-off-by: Ethan Zhao <haifeng.zhao@xxxxxxxxxxxxxxx>
---
 drivers/iommu/intel/dmar.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index 814134e9aa5a..e2d5ea2b0683 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1272,6 +1272,7 @@ 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 q_inval *qi = iommu->qi;
 	int shift = qi_shift(iommu);
 
@@ -1316,6 +1317,13 @@ 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");
 
@@ -1325,6 +1333,16 @@ 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 the same as
+		 * current ATS invalidation target device, if yes, don't try this
+		 * request anymore if the target device isn't present.
+		 * 0 value of ite_sid means old VT-d device, no ite_sid value.
+		 */
+		if (pdev && ite_sid && !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