Re: [PATCH 3/9] iommu: Add common code to handle IO page faults

[Jean-Philippe Brucker]

On Wed, Jul 12, 2023 at 10:32:13AM +0800, Baolu Lu wrote:
> > btw is there value of moving the group handling logic from
> > iommu_queue_iopf() to this common function?
> > 
> > I wonder whether there is any correctness issue if not forwarding
> > partial request to iommufd. If not this can also help reduce
> > notifications to the user until the group is ready.
> 
> I don't think there's any correctness issue. But it should be better if
> we can inject the page faults to vm guests as soon as possible. There's
> no requirement to put page requests to vIOMMU's hardware page request
> queue at the granularity of a fault group. Thoughts?

Not sure I understand you correctly, but we can't inject partial fault
groups: if the HW PRI queue overflows, the last fault in a group may be
lost, so the non-last faults in that group already injected won't be
completed (until PRGI reuse), leaking PRI request credits and guest
resources.

Thanks,
Jean