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Date:   Thu, 3 Jun 2021 11:19:14 -0700
From:   Jacob Pan <jacob.jun.pan@linux.intel.com>
To:     Shenming Lu <lushenming@huawei.com>
Cc:     Jason Gunthorpe <jgg@nvidia.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        David Woodhouse <dwmw2@infradead.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "Alex Williamson (alex.williamson@redhat.com)" 
        <alex.williamson@redhat.com>, Jason Wang <jasowang@redhat.com>,
        Eric Auger <eric.auger@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
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        Zenghui Yu <yuzenghui@huawei.com>,
        "wanghaibin.wang@huawei.com" <wanghaibin.wang@huawei.com>,
        jacob.jun.pan@linux.intel.com
Subject: Re: [RFC] /dev/ioasid uAPI proposal
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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.

> Thanks,
> Shenming
> 


Thanks,

Jacob