linux-kernel - RE: [PATCH v10 08/12] iommu/sva: Refactoring iommu_sva_bind/unbind

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Date:   Mon, 25 Jul 2022 07:50:52 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     Joerg Roedel <joro@...tes.org>,
        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>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Zhangfei Gao" <zhangfei.gao@...aro.org>,
        "Zhu, Tony" <tony.zhu@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v10 08/12] iommu/sva: Refactoring
 iommu_sva_bind/unbind_device()

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Sunday, July 24, 2022 9:48 PM
> >
> > The API is really refcounting the PASID:
> >
> >> +struct iommu_sva *iommu_sva_bind_device(struct device *dev,
> >> +					struct mm_struct *mm);
> >> +void iommu_sva_unbind_device(struct iommu_sva *handle);
> >
> > So what you need to do is store that 'iommu_sva' in the group's PASID
> > xarray.
> >
> > The bind logic would be
> >
> >    sva = xa_load(group->pasid, mm->pasid)
> >    if (sva)
> >       refcount_inc(sva->users)
> >       return sva
> >    sva = kalloc
> >    sva->domain = domain
> >    xa_store(group->pasid, sva);
> 
> Thanks for the suggestion. It makes a lot of sense to me.
> 
> Furthermore, I'd like to separate the generic data from the caller-
> specific things because the group->pasid_array should also be able to
> serve other usages. Hence, the attach/detach_device_pasid interfaces
> might be changed like below:
> 
> /* Collection of per-pasid IOMMU data */
> struct group_pasid {
> 	struct iommu_domain *domain;
> 	void *priv;
> };
> 

Is there any reason why pasid refcnt is sva specific and needs to be
in a priv field?