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Subject: Re: [RFC] /dev/ioasid uAPI proposal
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>
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From:   Shenming Lu <lushenming@huawei.com>
Message-ID: <eebe5926-efa0-8bab-e8d4-bd327669637f@huawei.com>
Date:   Fri, 4 Jun 2021 10:03:08 +0800
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On 2021/6/4 2:19, Jacob Pan wrote:
> Hi Shenming,
> 
> On Wed, 2 Jun 2021 12:50:26 +0800, Shenming Lu <lushenming@huawei.com>
> 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.

> 
> 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.

Yeah, and it can also be said that the provider of the page table registers the
handler (Baolu).

Thanks,
Shenming