linux-kernel - Re: [PATCH v2 2/8] iommu: Add attach/detach_dev

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Message-ID: <YjB4AyrgsnbUrlLe@myrica>
Date:   Tue, 15 Mar 2022 11:26:59 +0000
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>
Subject: Re: [PATCH v2 2/8] iommu: Add attach/detach_dev_pasid domain ops

On Mon, Mar 14, 2022 at 10:07:06PM -0700, Jacob Pan wrote:
> From: Lu Baolu <baolu.lu@...ux.intel.com>
> 
> An IOMMU domain represents an address space which can be attached by
> devices that perform DMA within a domain. However, for platforms with
> PASID capability the domain attachment needs be handled at device+PASID
> level. There can be multiple PASIDs within a device and multiple devices
> attached to a given domain.
> This patch introduces a new IOMMU op which support device, PASID, and
> IOMMU domain attachment. The immediate use case is for PASID capable
> devices to perform DMA under DMA APIs.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>  include/linux/iommu.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 369f05c2a4e2..fde5b933dbe3 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -227,6 +227,8 @@ struct iommu_iotlb_gather {
>   * @aux_get_pasid: get the pasid given an aux-domain
>   * @sva_bind: Bind process address space to device
>   * @sva_unbind: Unbind process address space from device
> + * @attach_dev_pasid: attach an iommu domain to a pasid of device
> + * @detach_dev_pasid: detach an iommu domain from a pasid of device

Isn't that operation "assign a PASID to a domain" instead?  In patch 5,
the domain is already attached to the device, so set_domain_pasid() might
be clearer and to the point. If the IOMMU driver did the allocation we
could also avoid patch 1.

If I understand correctly this series is not about a generic PASID API
that allows drivers to manage multiple DMA address spaces, because there
still doesn't seem to be any interest in that. It's about the specific
IDXD use-case, so let's focus on that. We can introduce a specialized call
such as (iommu|dma)_set_device_pasid(), which will be easy to consolidate
later into a more generic "dma_enable_pasid()" API if that ever seems
useful.

Thanks,
Jean

>   * @sva_get_pasid: Get PASID associated to a SVA handle
>   * @page_response: handle page request response
>   * @cache_invalidate: invalidate translation caches
> @@ -296,6 +298,10 @@ struct iommu_ops {
>  	struct iommu_sva *(*sva_bind)(struct device *dev, struct mm_struct *mm,
>  				      void *drvdata);
>  	void (*sva_unbind)(struct iommu_sva *handle);
> +	int (*attach_dev_pasid)(struct iommu_domain *domain,
> +				struct device *dev, ioasid_t id);
> +	void (*detach_dev_pasid)(struct iommu_domain *domain,
> +				 struct device *dev, ioasid_t id);
>  	u32 (*sva_get_pasid)(struct iommu_sva *handle);
>  
>  	int (*page_response)(struct device *dev,
> -- 
> 2.25.1
>