linux-kernel - Re: [PATCH v2 07/10] iommu: Use right way to retrieve iommu

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Date:   Wed, 9 Feb 2022 09:33:55 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 07/10] iommu: Use right way to retrieve iommu_ops

On Tue, Feb 08, 2022 at 09:25:56AM +0800, Lu Baolu wrote:
> The common iommu_ops is hooked to both device and domain. When a helper
> has both device and domain pointer, the way to get the iommu_ops looks
> messy in iommu core. This sorts out the way to get iommu_ops. The device
> related helpers go through device pointer, while the domain related ones
> go through domain pointer.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  include/linux/iommu.h | 14 ++++++++++++++
>  drivers/iommu/iommu.c | 20 +++++++++++---------
>  2 files changed, 25 insertions(+), 9 deletions(-)
 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 9ffa2e88f3d0..eb2684f95018 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -381,6 +381,20 @@ static inline void iommu_iotlb_gather_init(struct iommu_iotlb_gather *gather)
>  	};
>  }
>  
> +static inline const struct iommu_ops *dev_iommu_ops(struct device *dev)
> +{
> +	/*
> +	 * Assume that valid ops must be installed if iommu_probe_device()
> +	 * has succeeded. The device ops are essentially for internal use
> +	 * within the IOMMU subsystem itself, so we should be able to trust
> +	 * ourselves not to misuse the helper.
> +	 */
> +	WARN_ON(!dev || !dev->iommu || !dev->iommu->iommu_dev ||
> +		!dev->iommu->iommu_dev->ops);

IMHO this is overzealous. The kernel will reliably crash on null
dereference here, I'm not sure this adds much. But either way:

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason