linux-kernel - Re: [PATCH v2 6/7] iommu/dma: Centralise iommu_setup_dma

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Date: Sun, 17 Dec 2023 09:06:51 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Robin Murphy <robin.murphy@....com>
Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Joerg Roedel <joro@...tes.org>, Christoph Hellwig <hch@....de>,
	Vineet Gupta <vgupta@...nel.org>,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Hanjun Guo <guohanjun@...wei.com>,
	Sudeep Holla <sudeep.holla@....com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	David Woodhouse <dwmw2@...radead.org>,
	Lu Baolu <baolu.lu@...ux.intel.com>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Matthew Rosato <mjrosato@...ux.ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
	Rob Herring <robh+dt@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-acpi@...r.kernel.org, iommu@...ts.linux.dev,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 6/7] iommu/dma: Centralise iommu_setup_dma_ops()

On Thu, Dec 14, 2023 at 06:22:49PM +0000, Robin Murphy wrote:

> Taking yet another look, there's not actually one single place we can do
> this right now which will work in a manageable way for all cases.

The dma ops should be set after changing the translation and there is
only one place that attachs the domain? What prevents putting it
there?

> @@ -3217,18 +3220,9 @@ static ssize_t iommu_group_store_type(struct iommu_group *group,
>  	if (ret)
>  		goto out_unlock;
> -	/*
> -	 * Release the mutex here because ops->probe_finalize() call-back of
> -	 * some vendor IOMMU drivers calls arm_iommu_attach_device() which
> -	 * in-turn might call back into IOMMU core code, where it tries to take
> -	 * group->mutex, resulting in a deadlock.
> -	 */
> -	mutex_unlock(&group->mutex);
> -
>  	/* Make sure dma_ops is appropriatley set */
>  	for_each_group_device(group, gdev)
> -		iommu_group_do_probe_finalize(gdev->dev);
> -	return count;

If we are turning this into something that only works for the ARM DMA
then the remaining caller should be guarded by an IS_ENABLED

Jason