linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Message-ID: <20210603111914.653c4f61@jacob-builder>
Date:   Thu, 3 Jun 2021 11:19:14 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Shenming Lu <lushenming@...wei.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>, Jason Wang <jasowang@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Robin Murphy" <robin.murphy@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        "wanghaibin.wang@...wei.com" <wanghaibin.wang@...wei.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC] /dev/ioasid uAPI proposal

Hi Shenming,

On Wed, 2 Jun 2021 12:50:26 +0800, Shenming Lu <lushenming@...wei.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