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

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Date:   Tue, 15 Mar 2022 11:49:57 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
CC:     "iommu@...ts.linux-foundation.org" <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>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Subject: RE: [PATCH v2 2/8] iommu: Add attach/detach_dev_pasid domain ops

> From: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Sent: Tuesday, March 15, 2022 7:27 PM
> 
> 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.

iiuc this API can also work for future SIOV usage where each mdev attached
to the domain has its own pasid. "assigning a PASID to a domain" sounds
like going back to the previous aux domain approach which has one PASID
per domain and that PASID is used on all devices attached to the aux domain...

> 
> 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
> >