Re: [PATCH v5 08/18] iommu/arm-smmu-v3: Skip remaining GERROR causes on SFM

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Calling `arm_smmu_device_disable()` from the `arm_smmu_gerror_handler` hardirq handler triggers a sleep-in-atomic BUG because it polls a register with a non-zero sleep delay.
--

commit 1a84214c7c4ffc13f27088bf53ea902723185640
Author: Nicolin Chen <nicolinc@nvidia.com>

iommu/arm-smmu-v3: Skip remaining GERROR causes on SFM

When the SMMU enters Service Failure Mode (SFM), the remaining GERROR
causes are skipped and acked early since the SMMU is being disabled.

> 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 da29e523d78b7..8a4edefeec770 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2315,8 +2315,11 @@ static irqreturn_t arm_smmu_gerror_handler(int irq, void *dev)
>  		 active);
>  
>  	if (active & GERROR_SFM_ERR) {
> +		/* SMMU is being disabled, so other errors don't matter */
> +		writel(gerror, smmu->base + ARM_SMMU_GERRORN);
>  		dev_err(smmu->dev, "device has entered Service Failure Mode!\n");
>  		arm_smmu_device_disable(smmu);

[Severity: High]
This is a pre-existing issue, but does calling arm_smmu_device_disable()
from the arm_smmu_gerror_handler() hardirq handler trigger a 
sleep-in-atomic BUG?

arm_smmu_device_disable() eventually calls arm_smmu_write_reg_sync(),
which uses readl_relaxed_poll_timeout() with a 1us delay:

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c:arm_smmu_write_reg_sync() {
    ...
    return readl_relaxed_poll_timeout(smmu->base + ack_off, reg, reg == val,
                                      1, ARM_SMMU_POLL_TIMEOUT_US);
}

The polling macro invokes might_sleep_if(1) and usleep_range(), which isn't
safe in hardirq context.

> +		return IRQ_HANDLED;
>  	}
>  
>  	if (active & GERROR_MSI_GERROR_ABT_ERR)

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1783044582.git.nicolinc@nvidia.com?part=8