linux-kernel - Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid

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Message-ID: <20220512120303.GY49344@nvidia.com>
Date:   Thu, 12 May 2022 09:03:03 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        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>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid_dev in SVA
 interfaces

On Thu, May 12, 2022 at 07:59:41PM +0800, Baolu Lu wrote:
> On 2022/5/12 19:48, Jason Gunthorpe wrote:
> > On Thu, May 12, 2022 at 01:17:08PM +0800, Baolu Lu wrote:
> > > On 2022/5/12 13:01, Tian, Kevin wrote:
> > > > > From: Baolu Lu <baolu.lu@...ux.intel.com>
> > > > > Sent: Thursday, May 12, 2022 11:03 AM
> > > > > 
> > > > > On 2022/5/11 22:53, Jason Gunthorpe wrote:
> > > > > > > > Also, given the current arrangement it might make sense to have a
> > > > > > > > struct iommu_domain_sva given that no driver is wrappering this in
> > > > > > > > something else.
> > > > > > > Fair enough. How about below wrapper?
> > > > > > > 
> > > > > > > +struct iommu_sva_domain {
> > > > > > > +       /*
> > > > > > > +        * Common iommu domain header,*must*  be put at the top
> > > > > > > +        * of the structure.
> > > > > > > +        */
> > > > > > > +       struct iommu_domain domain;
> > > > > > > +       struct mm_struct *mm;
> > > > > > > +       struct iommu_sva bond;
> > > > > > > +}
> > > > > > > 
> > > > > > > The refcount is wrapped in bond.
> > > > > > I'm still not sure that bond is necessary
> > > > > 
> > > > > "bond" is the sva handle that the device drivers get through calling
> > > > > iommu_sva_bind().
> > > > > 
> > > > 
> > > > 'bond' was required before because we didn't have a domain to wrap
> > > > the page table at that time.
> > > > 
> > > > Now we have a domain and it is 1:1 associated to bond. Probably
> > > > make sense now by just returning the domain as the sva handle
> > > > instead?
> > > 
> > > It also includes the device information that the domain has been
> > > attached. So the sva_unbind() looks like this:
> > > 
> > > /**
> > >   * iommu_sva_unbind_device() - Remove a bond created with
> > > iommu_sva_bind_device
> > >   * @handle: the handle returned by iommu_sva_bind_device()
> > >   *
> > >   * Put reference to a bond between device and address space. The device
> > > should
> > >   * not be issuing any more transaction for this PASID. All outstanding page
> > >   * requests for this PASID must have been flushed to the IOMMU.
> > >   */
> > > void iommu_sva_unbind_device(struct iommu_sva *handle)
> > > 
> > > It's fine to replace the iommu_sva with iommu_sva_domain for sva handle,
> > > if we can include the device in the unbind() interface.
> > 
> > Why would we have a special unbind for SVA?
> 
> It's about SVA kAPI for device drivers. The existing kAPIs include:
> 
> struct iommu_sva *iommu_sva_bind_device(struct device *dev,
>                                         struct mm_struct *mm,
>                                         void *drvdata);
> void iommu_sva_unbind_device(struct iommu_sva *handle);
> u32 iommu_sva_get_pasid(struct iommu_sva *handle);

This is not what we agreed the API should be. We agreed:

 iommu_sva_domain_alloc()
 iommu_attach_device_pasid()
 iommu_detach_device_pasid()

Again, SVA should not be different from normal domain stuff.

Jason