linux-kernel - Re: [PATCH] xen/grant-dma-iommu: Implement a dummy probe

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Date:   Fri, 10 Feb 2023 15:32:53 -0800 (PST)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Oleksandr Tyshchenko <olekstysh@...il.com>
cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH] xen/grant-dma-iommu: Implement a dummy probe_device()
 callback

On Wed, 8 Feb 2023, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
> 
> Update stub IOMMU driver (which main purpose is to reuse generic
> IOMMU device-tree bindings by Xen grant DMA-mapping layer on Arm)
> according to the recent changes done in the following
> commit 57365a04c921 ("iommu: Move bus setup to IOMMU device registration").
> 
> With probe_device() callback being called during IOMMU device registration,
> the uninitialized callback just leads to the "kernel NULL pointer
> dereference" issue during boot. Fix that by adding a dummy callback.
> 
> Looks like the release_device() callback is not mandatory to be
> implemented as IOMMU framework makes sure that callback is initialized
> before dereferencing.
> 
> Reported-by: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>

Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>


> ---
>  drivers/xen/grant-dma-iommu.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/grant-dma-iommu.c b/drivers/xen/grant-dma-iommu.c
> index 16b8bc0c0b33..6a9fe02c6bfc 100644
> --- a/drivers/xen/grant-dma-iommu.c
> +++ b/drivers/xen/grant-dma-iommu.c
> @@ -16,8 +16,15 @@ struct grant_dma_iommu_device {
>  	struct iommu_device iommu;
>  };
>  
> -/* Nothing is really needed here */
> -static const struct iommu_ops grant_dma_iommu_ops;
> +static struct iommu_device *grant_dma_iommu_probe_device(struct device *dev)
> +{
> +	return ERR_PTR(-ENODEV);
> +}
> +
> +/* Nothing is really needed here except a dummy probe_device callback */
> +static const struct iommu_ops grant_dma_iommu_ops = {
> +	.probe_device = grant_dma_iommu_probe_device,
> +};
>  
>  static const struct of_device_id grant_dma_iommu_of_match[] = {
>  	{ .compatible = "xen,grant-dma" },
> -- 
> 2.34.1
>