RE: [PATCH rc v4 5/5] iommu/arm-smmu-v3: Detect ARM_SMMU_OPT_KDUMP_ADOPT in probe()

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Sent: Wednesday, April 29, 2026 3:21 PM
> 
> arm_smmu_device_hw_probe() runs before arm_smmu_init_structures(), so
> it's
> natural to decide whether the kdump kernel must adopt the crashed kernel's
> stream table.
> 
> Given that memremap is used to adopt the old stream table, set this option
> only on a coherent SMMU.
> 
> And make sure SMMU isn't in Service Failure Mode.
> 
> 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>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with nits:

> 
> +static void arm_smmu_device_hw_probe_kdump(struct arm_smmu_device
> *smmu)
> +{
> +	u32 gerror, gerrorn, active;
> +
> +	/*
> +	 * If SMMU is already active in kdump case, there could be in-flight
> DMA
> +	 * from devices initiated by the crashed kernel.
> +	 */
> +	if (!(readl_relaxed(smmu->base + ARM_SMMU_CR0) &
> CR0_SMMUEN))
> +		return;

Above comment is for the entire function. for the check here the comment
should be that no in-fly DMA to require adoption due to SMMU disabled.

> +
> +	/* For now, only support a coherent SMMU that works with
> MEMREMAP_WB */
> +	if (!(smmu->features & ARM_SMMU_FEAT_COHERENCY)) {
> +		dev_warn(smmu->dev,
> +			 "kdump: non-coherent SMMU can't adopt stream
> table\n");

"can't adopt stream table so SMMU will be reset to block all DMAs"