Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid_dev in SVA interfaces

[Baolu Lu]

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@xxxxxxxxxxxxxxx>
> > > > 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);

> SVA should not different from normal domains it should use the normal
> detach flow too.

Best regards,
baolu