[PATCH rc v1 3/4] iommu/arm-smmu-v3: Retain SMMUEN during kdump device reset

[Nicolin Chen]

When ARM_SMMU_OPT_KDUMP is set, skip the GBPA/disable/CR1/CR2/STRTAB_BASE
update sequence in arm_smmu_device_reset(). Those register writes are all
CONSTRAINED UNPREDICTABLE while SMMUEN==1, so leaving them untouched lets
in-flight DMA continue to be translated by the adopted stream table.

Initialize 'enables' to 0 so it can carry CR0_SMMUEN in kdump case. Then,
preserve that when enabling the command queue.

Also add a comment explaining why EVTQ/PRIQ are disabled in kdump cases.

Fixes: b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions if SMMU is enabled in kdump kernel")
Cc: stable@xxxxxxxxxxxxxxx # v6.12+
Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 35 +++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index ff3c1beb3739e..d0ef8fb876978 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -4931,13 +4931,28 @@ static void arm_smmu_write_strtab(struct arm_smmu_device *smmu)
 static int arm_smmu_device_reset(struct arm_smmu_device *smmu)
 {
 	int ret;
-	u32 reg, enables;
+	u32 reg, enables = 0;
 	struct arm_smmu_cmdq_ent cmd;
 
 	/* Clear CR0 and sync (disables SMMU and queue processing) */
 	reg = readl_relaxed(smmu->base + ARM_SMMU_CR0);
 	if (reg & CR0_SMMUEN) {
 		dev_warn(smmu->dev, "SMMU currently enabled! Resetting...\n");
+
+		/*
+		 * In a kdump case, retain SMMUEN to avoid transiently aborting
+		 * in-flight DMA. According to spec, updating STRTAB_BASE, CR1,
+		 * or CR2 while SMMUEN==1 is CONSTRAINED UNPREDICTABLE. So skip
+		 * those register updates and rely on the adopted stream table
+		 * from the crashed kernel.
+		 */
+		if (smmu->options & ARM_SMMU_OPT_KDUMP) {
+			dev_info(smmu->dev,
+				 "kdump: retaining SMMUEN for in-flight DMA\n");
+			enables = CR0_SMMUEN;
+			goto reset_queues;
+		}
+
 		arm_smmu_update_gbpa(smmu, GBPA_ABORT, 0);
 	}
 
@@ -4965,12 +4980,23 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu)
 	/* Stream table */
 	arm_smmu_write_strtab(smmu);
 
+reset_queues:
+	if (smmu->options & ARM_SMMU_OPT_KDUMP) {
+		/* Disable queues since arm_smmu_device_disable() was skipped */
+		ret = arm_smmu_write_reg_sync(smmu, enables, ARM_SMMU_CR0,
+					      ARM_SMMU_CR0ACK);
+		if (ret) {
+			dev_err(smmu->dev, "failed to disable queues\n");
+			return ret;
+		}
+	}
+
 	/* Command queue */
 	writeq_relaxed(smmu->cmdq.q.q_base, smmu->base + ARM_SMMU_CMDQ_BASE);
 	writel_relaxed(smmu->cmdq.q.llq.prod, smmu->base + ARM_SMMU_CMDQ_PROD);
 	writel_relaxed(smmu->cmdq.q.llq.cons, smmu->base + ARM_SMMU_CMDQ_CONS);
 
-	enables = CR0_CMDQEN;
+	enables |= CR0_CMDQEN;
 	ret = arm_smmu_write_reg_sync(smmu, enables, ARM_SMMU_CR0,
 				      ARM_SMMU_CR0ACK);
 	if (ret) {
@@ -5038,6 +5064,11 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu)
 		return ret;
 	}
 
+	/*
+	 * Disable EVTQ and PRIQ in kdump kernel. The old kernel's CDs and page
+	 * tables may be corrupted, which could trigger event spamming. PRIQ is
+	 * also useless since we cannot service page requests during kdump.
+	 */
 	if (is_kdump_kernel())
 		enables &= ~(CR0_EVTQEN | CR0_PRIQEN);
 
-- 
2.43.0