Re: [PATCH RFC 10/11] iommu: Make IOPF handling framework generic

[Jean-Philippe Brucker]

Hi Kevin,

On Mon, Mar 21, 2022 at 08:09:36AM +0000, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Sunday, March 20, 2022 2:40 PM
> > 
> > The existing IOPF handling framework only handles the I/O page faults for
> > SVA. Ginven that we are able to link iommu domain with each I/O page fault,
> > we can now make the I/O page fault handling framework more general for
> > more types of page faults.
> 
> "make ... generic" in subject line is kind of confusing. Reading this patch I
> think you really meant changing from per-device fault handling to per-domain
> fault handling. This is more accurate in concept since the fault is caused by
> the domain page table. 😊

I tend to disagree with that last part. The fault is caused by a specific
device accessing shared page tables. We should keep that device
information throughout the fault handling, so that we can report it to the
driver when things go wrong. A process can have multiple threads bound to
different devices, they share the same mm so if the driver wanted to
signal a misbehaving thread, similarly to a SEGV on the CPU side, it would
need the device information to precisely report it to userspace.

Thanks,
Jean