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

Nicolin Chen
2026-04-09T19:47:29Z

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@vger.kernel.org # v6.12+
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
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