linux-kernel - RE: [PATCH v9 04/11] iommu: Add sva iommu

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Date:   Mon, 27 Jun 2022 08:29:21 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Jiang, Dave" <dave.jiang@...el.com>, Vinod Koul <vkoul@...nel.org>
CC:     Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.org>
Subject: RE: [PATCH v9 04/11] iommu: Add sva iommu_domain support

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, June 21, 2022 10:44 PM
> 
> The sva iommu_domain represents a hardware pagetable that the IOMMU
> hardware could use for SVA translation. This adds some infrastructure
> to support SVA domain in the iommu common layer. It includes:
> 
> - Extend the iommu_domain to support a new IOMMU_DOMAIN_SVA
> domain
>   type. The IOMMU drivers that support SVA should provide the sva
>   domain specific iommu_domain_ops.
> - Add a helper to allocate an SVA domain. The iommu_domain_free()
>   is still used to free an SVA domain.
> - Add helpers to attach an SVA domain to a device and the reverse
>   operation.
> 
> Some buses, like PCI, route packets without considering the PASID value.
> Thus a DMA target address with PASID might be treated as P2P if the
> address falls into the MMIO BAR of other devices in the group. To make
> things simple, the attach/detach interfaces only apply to devices
> belonging to the singleton groups, and the singleton is immutable in
> fabric i.e. not affected by hotplug.
> 
> The iommu_attach/detach_device_pasid() can be used for other purposes,
> such as kernel DMA with pasid, mediation device, etc.

I'd split this into two patches. One for adding iommu_attach/
detach_device_pasid() and set/block_dev_pasid ops, and the
other for adding SVA.

>  struct iommu_domain {
>  	unsigned type;
>  	const struct iommu_domain_ops *ops;
>  	unsigned long pgsize_bitmap;	/* Bitmap of page sizes in use */
> -	iommu_fault_handler_t handler;
> -	void *handler_token;
>  	struct iommu_domain_geometry geometry;
>  	struct iommu_dma_cookie *iova_cookie;
> +	union {
> +		struct {	/* IOMMU_DOMAIN_DMA */
> +			iommu_fault_handler_t handler;
> +			void *handler_token;
> +		};

why is it DMA domain specific? What about unmanaged 
domain? Unrecoverable fault can happen on any type
including SVA. Hence I think above should be domain type
agnostic.

> +		struct {	/* IOMMU_DOMAIN_SVA */
> +			struct mm_struct *mm;
> +		};
> +	};
>  };
> 



> +
> +struct iommu_domain *iommu_sva_domain_alloc(struct device *dev,
> +					    struct mm_struct *mm)
> +{
> +	const struct iommu_ops *ops = dev_iommu_ops(dev);
> +	struct iommu_domain *domain;
> +
> +	domain = ops->domain_alloc(IOMMU_DOMAIN_SVA);
> +	if (!domain)
> +		return NULL;
> +
> +	domain->type = IOMMU_DOMAIN_SVA;

It's a bit weird that the type has been specified when calling
ops->domain_alloc while it still leaves to the caller to set the
type. But this is not caused by this series. could be cleaned
up separately.

> +
> +	mutex_lock(&group->mutex);
> +	curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain,
> GFP_KERNEL);
> +	if (curr)
> +		goto out_unlock;

Need check xa_is_err(old).