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

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2023/7/12 17:45, Jean-Philippe Brucker wrote:
> 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.

Yeah, that's how vIOMMU injects the faults. On host/hypervisor side, my
understanding is that faults should be uploaded as soon as possible.

Best regards,
baolu