RE: [RFC] /dev/ioasid uAPI proposal

[Liu, Yi L]

> From: Shenming Lu <lushenming@xxxxxxxxxx>
> Sent: Friday, June 4, 2021 10:03 AM
> 
> On 2021/6/4 2:19, Jacob Pan wrote:
> > 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.
> 
> Yeah, I also proposed this before, registering the handler in the
> BIND_PGTABLE
> ioctl does make sense for the guest page faults. :-)
> 
> But how about the page faults from the GPA address space (it's page table is
> mapped through the MAP_DMA ioctl)? From your point of view, it seems
> that we should register the handler for the GPA address space in the (first)
> MAP_DMA ioctl.

under new proposal, I think the page fault handler is also registered
per ioasid object. The difference compared with guest page table case
is there is no need to inject the fault to VM.
 
Regards,
Yi Liu