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Subject: Re: [RFC] /dev/ioasid uAPI proposal
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Shenming Lu <lushenming@huawei.com>
Cc:     Jason Gunthorpe <jgg@nvidia.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <1175ebd5-9d8e-2000-6d05-baa93e960915@redhat.com>
Date:   Fri, 4 Jun 2021 09:30:37 +0800
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?? 2021/6/4 ????2:19, Jacob Pan д??:
> 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.
>
> 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.


As discussed in another thread.

I think the reason is that ATS doesn't forbid the #PF to be reported via 
a device specific way.

Thanks


>
>> Thanks,
>> Shenming
>>
>
> Thanks,
>
> Jacob
>