[PATCH rc v3 3/5] iommu/arm-smmu-v3: Retain CR0_SMMUEN during kdump device reset

Nicolin Chen
2026-04-25T21:32:16Z

When ARM_SMMU_OPT_KDUMP_ADOPT is detected, do not disable SMMUEN and skip
the CR1/CR2/STRTAB_BASE update sequence in arm_smmu_device_reset(). Those
register writes are all CONSTRAINED UNPREDICTABLE while CR0_SMMUEN==1, so
leaving them intact lets in-flight DMAs 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.

Clear latched gerror bits if necessary.

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 | 47 +++++++++++++++++++--
1 file changed, 44 insertions(+), 3 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 8423bcc4be69e..b6aade469a6b6 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -5017,11 +5017,28 @@ 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);
+
+ /*
+ * In a kdump case (set when CR0_SMMUEN=1 and !GERROR_SFM_ERR), retain
+ * CR0_SMMUEN to avoid aborting in-flight DMA, and CR0_ATSCHK to carry
+ * on the ATS-check policy.
+ *
+ * According to spec, updating STRTAB_BASE/CR1/CR2 when CR0_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_ADOPT) {
+ dev_info(smmu->dev,
+ "kdump: retaining SMMUEN for in-flight DMA\n");
+ enables = reg & (CR0_SMMUEN | CR0_ATSCHK);
+ goto reset_queues;
+ }
+
+ /* Clear CR0 and sync (disables SMMU and queue processing) */
if (reg & CR0_SMMUEN) {
dev_warn(smmu->dev, "SMMU currently enabled! Resetting...\n");
arm_smmu_update_gbpa(smmu, GBPA_ABORT, 0);
@@ -5051,12 +5068,36 @@ 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_ADOPT) {
+ /* 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;
+ }
+ }
+
+ /*
+ * GERROR bits are latched. Read after queue disabling so that unhandled
+ * errors would be visible. Ack everything prior to re-enabling the CMDQ
+ * as a stale CMDQ_ERR would halt the CMDQ and new command will timeout.
+ */
+ if (is_kdump_kernel()) {
+ u32 gerror = readl_relaxed(smmu->base + ARM_SMMU_GERROR);
+ u32 gerrorn = readl_relaxed(smmu->base + ARM_SMMU_GERRORN);
+
+ if ((gerror ^ gerrorn) & GERROR_ERR_MASK)
+ writel(gerror, smmu->base + ARM_SMMU_GERRORN);
+ }
+
/* 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) {
--
2.43.0