Re: [PATCH v2 6/7] iommu/dma: Centralise iommu_setup_dma_ops() - Jean-Philippe Brucker

From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>, Christoph Hellwig <hch@lst.de>,
	Vineet Gupta <vgupta@kernel.org>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Huacai Chen <chenhuacai@kernel.org>,
	WANG Xuerui <kernel@xen0n.name>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Hanjun Guo <guohanjun@huawei.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Niklas Schnelle <schnelle@linux.ibm.com>,
	Matthew Rosato <mjrosato@linux.ibm.com>,
	Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
	Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org,
	iommu@lists.linux.dev, devicetree@vger.kernel.org
Subject: Re: [PATCH v2 6/7] iommu/dma: Centralise iommu_setup_dma_ops()
Date: Thu, 14 Dec 2023 16:51:26 +0000	[thread overview]
Message-ID: <20231214165126.GA3726750@myrica> (raw)
In-Reply-To: <5d89190b35720bf5b66621f46b6d3c85323d8eab.1702486837.git.robin.murphy@arm.com>

On Wed, Dec 13, 2023 at 05:17:59PM +0000, Robin Murphy wrote:
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 27a167f4cd3e..d808c8dcf5cb 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1724,25 +1724,20 @@ static const struct dma_map_ops iommu_dma_ops = {
>  	.opt_mapping_size	= iommu_dma_opt_mapping_size,
>  };
>  
> -/*
> - * The IOMMU core code allocates the default DMA domain, which the underlying
> - * IOMMU driver needs to support via the dma-iommu layer.
> - */
> -void iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64 dma_limit)
> +void iommu_setup_dma_ops(struct device *dev)
>  {
>  	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
>  
> -	if (!domain)
> -		goto out_err;
> +	if (dev_is_pci(dev))
> +		dev->iommu->pci_32bit_workaround = !iommu_dma_forcedac;
>  
> -	/*
> -	 * The IOMMU core code allocates the default DMA domain, which the
> -	 * underlying IOMMU driver needs to support via the dma-iommu layer.
> -	 */
>  	if (iommu_is_dma_domain(domain)) {

...

> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 824989874dee..43f630d0530e 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -560,10 +560,10 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list
>  		if (list_empty(&group->entry))
>  			list_add_tail(&group->entry, group_list);
>  	}
> -	mutex_unlock(&group->mutex);
>  
> -	if (dev_is_pci(dev))
> -		iommu_dma_set_pci_32bit_workaround(dev);
> +	iommu_setup_dma_ops(dev);

With Intel VT-d (QEMU emulation) I get a crash in iommu_setup_dma_ops()
because at this point group->domain and group->default_domain are still
NULL, group_list is non-NULL.

No problem with x86 virtio-iommu, it goes through
iommu_setup_default_domain() earlier in the function. Arm virtio-iommu is
fine too.

Thanks,
Jean

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