Re: [RFC] /dev/ioasid uAPI proposal

[Jason Gunthorpe]

On Fri, Jun 04, 2021 at 09:22:43AM -0700, Jacob Pan wrote:
> Hi Jason,
> 
> On Fri, 4 Jun 2021 09:30:37 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> 
> > 在 2021/6/4 上午2:19, Jacob Pan 写道:
> > > Hi Shenming,
> > >
> > > On Wed, 2 Jun 2021 12:50:26 +0800, Shenming Lu <lushenming@xxxxxxxxxx>
> > > wrote:
> > >  
> > >> On 2021/6/2 1:33, Jason Gunthorpe wrote:  
> > >>> On Tue, Jun 01, 2021 at 08:30:35PM +0800, Lu Baolu wrote:
> > >>>      
> > >>>> The drivers register per page table fault handlers to /dev/ioasid
> > >>>> which will then register itself to iommu core to listen and route
> > >>>> the per- device I/O page faults.  
> > >>> I'm still confused why drivers need fault handlers at all?  
> > >> Essentially it is the userspace that needs the fault handlers,
> > >> one case is to deliver the faults to the vIOMMU, and another
> > >> case is to enable IOPF on the GPA address space for on-demand
> > >> paging, it seems that both could be specified in/through the
> > >> IOASID_ALLOC ioctl?
> > >>  
> > > I would think IOASID_BIND_PGTABLE is where fault handler should be
> > > registered. There wouldn't be any IO page fault without the binding
> > > anyway.
> > >
> > > I also don't understand why device drivers should register the fault
> > > handler, the fault is detected by the pIOMMU and injected to the
> > > vIOMMU. So I think it should be the IOASID itself register the handler.
> > >  
> > 
> > 
> > As discussed in another thread.
> > 
> > I think the reason is that ATS doesn't forbid the #PF to be reported via 
> > a device specific way.
> 
> Yes, in that case we should support both. Give the device driver a chance
> to handle the IOPF if it can.

Huh?

The device driver does not "handle the IOPF" the device driver might
inject the IOPF.

Jason