linux-kernel - Re: [PATCH] iommu/rockchip: prevent iommus dead loop when two masters share one IOMMU

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Message-ID: <340d76b8-c3a6-4116-ae51-ac4e4ee6a994@arm.com>
Date: Fri, 20 Jun 2025 12:19:28 +0100
From: Robin Murphy <robin.murphy@....com>
To: Simon Xue <xxm@...k-chips.com>, joro@...tes.org, will@...nel.org,
 heiko@...ech.de
Cc: iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/rockchip: prevent iommus dead loop when two masters
 share one IOMMU

On 2025-06-20 8:39 am, Simon Xue wrote:
> When two masters share an IOMMU, calling ops->of_xlate during
> the second master's driver init may overwrite iommu->domain set
> by the first. This causes the check if (iommu->domain == domain)
> in rk_iommu_attach_device() to fail, resulting in the same
> iommu->node being added twice to &rk_domain->iommus, which can
> lead to an infinite loop in subsequent &rk_domain->iommus operations.

Indeed this is a property of the IOMMU instance itself so it really 
should be initialised before registration, irrespective of client 
devices. FWIW, if it's possible to take an unexpected 
RK_MMU_IRQ_PAGE_FAULT immediately after requesting the IRQ (e.g. in a 
kdump kernel after a crash with the hardware still running) then I think 
the current code could probably end up dereferencing NULL in 
report_iommu_fault() as well.

Reviewed-by: Robin Murphy <robin.murphy@....com>

And probably also:

Cc: stable@...r.kernel.org
Fixes: 25c2325575cc ("iommu/rockchip: Add missing set_platform_dma_ops 
callback")

Thanks,
Robin.

> Signed-off-by: Simon Xue <xxm@...k-chips.com>
> ---
>   drivers/iommu/rockchip-iommu.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
> index 22f74ba33a0e..e6bb3c784017 100644
> --- a/drivers/iommu/rockchip-iommu.c
> +++ b/drivers/iommu/rockchip-iommu.c
> @@ -1157,7 +1157,6 @@ static int rk_iommu_of_xlate(struct device *dev,
>   		return -ENOMEM;
>   
>   	data->iommu = platform_get_drvdata(iommu_dev);
> -	data->iommu->domain = &rk_identity_domain;
>   	dev_iommu_priv_set(dev, data);
>   
>   	platform_device_put(iommu_dev);
> @@ -1195,6 +1194,8 @@ static int rk_iommu_probe(struct platform_device *pdev)
>   	if (!iommu)
>   		return -ENOMEM;
>   
> +	iommu->domain = &rk_identity_domain;
> +
>   	platform_set_drvdata(pdev, iommu);
>   	iommu->dev = dev;
>   	iommu->num_mmu = 0;