Re: [PATCH rc v6 4/7] iommu/arm-smmu-v3: Skip EVTQ/PRIQ setup in kdump kernel

[Pranjal Shrivastava <praan@google.com>]

On Wed, May 20, 2026 at 10:03:21AM -0700, Nicolin Chen wrote:
> In kdump cases, the crashed kernel's CDs and page tables can be corrupted,
> which could trigger event spamming. Also, we cannot serve page requests.
> 
> Skip the EVTQ/PRIQ setup entirely rather than enabling then disabling them.
> 
> Also add some inline comments explaining that.
> 
> Fixes: b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions if SMMU is enabled in kdump kernel")
> Cc: stable@vger.kernel.org # v6.12+
> Suggested-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 43 +++++++++++++--------
>  1 file changed, 27 insertions(+), 16 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 e00b28e36f9c4..3f22949391c82 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -5161,21 +5161,35 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu)
>  	cmd.opcode = CMDQ_OP_TLBI_NSNH_ALL;
>  	arm_smmu_cmdq_issue_cmd_with_sync(smmu, &cmd);
>  
> -	/* Event queue */
> -	writeq_relaxed(smmu->evtq.q.q_base, smmu->base + ARM_SMMU_EVTQ_BASE);
> -	writel_relaxed(smmu->evtq.q.llq.prod, smmu->page1 + ARM_SMMU_EVTQ_PROD);
> -	writel_relaxed(smmu->evtq.q.llq.cons, smmu->page1 + ARM_SMMU_EVTQ_CONS);
> -
> -	enables |= CR0_EVTQEN;
> -	ret = arm_smmu_write_reg_sync(smmu, enables, ARM_SMMU_CR0,
> -				      ARM_SMMU_CR0ACK);
> -	if (ret) {
> -		dev_err(smmu->dev, "failed to enable event queue\n");
> -		return ret;
> +	/*
> +	 * Event queue
> +	 *
> +	 * Do not enable in a kdump case, as the crashed kernel's CDs and page
> +	 * tables might be corrupted, triggering event spamming.
> +	 */
> +	if (!is_kdump_kernel()) {
> +		writeq_relaxed(smmu->evtq.q.q_base,
> +			       smmu->base + ARM_SMMU_EVTQ_BASE);
> +		writel_relaxed(smmu->evtq.q.llq.prod,
> +			       smmu->page1 + ARM_SMMU_EVTQ_PROD);
> +		writel_relaxed(smmu->evtq.q.llq.cons,
> +			       smmu->page1 + ARM_SMMU_EVTQ_CONS);
> +
> +		enables |= CR0_EVTQEN;
> +		ret = arm_smmu_write_reg_sync(smmu, enables, ARM_SMMU_CR0,
> +					      ARM_SMMU_CR0ACK);

Nit:
I believe only the write_reg_sync(CR0) should be under this if condition
do we see any weird behavior if we perform the reg writes in
kdump_kernel?

> +		if (ret) {
> +			dev_err(smmu->dev, "failed to enable event queue\n");
> +			return ret;
> +		}
>  	}
>  
> -	/* PRI queue */
> -	if (smmu->features & ARM_SMMU_FEAT_PRI) {
> +	/*
> +	 * PRI queue
> +	 *
> +	 * Do not enable in a kdump case, as we cannot serve page requests.
> +	 */
> +	if (!is_kdump_kernel() && (smmu->features & ARM_SMMU_FEAT_PRI)) {
>  		writeq_relaxed(smmu->priq.q.q_base,
>  			       smmu->base + ARM_SMMU_PRIQ_BASE);
>  		writel_relaxed(smmu->priq.q.llq.prod,
> @@ -5208,9 +5222,6 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu)
>  		return ret;
>  	}
>  
> -	if (is_kdump_kernel())
> -		enables &= ~(CR0_EVTQEN | CR0_PRIQEN);
> -
>  	/* Enable the SMMU interface */
>  	enables |= CR0_SMMUEN;
>  	ret = arm_smmu_write_reg_sync(smmu, enables, ARM_SMMU_CR0,
> -- 
> 2.43.0
> 

Apart from that nit, 

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan