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

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Message-ID: <20210604162200.GA415775@nvidia.com>
Date:   Fri, 4 Jun 2021 13:22:00 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Shenming Lu <lushenming@...wei.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>, 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>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On Fri, Jun 04, 2021 at 09:22:43AM -0700, Jacob Pan wrote:
> Hi Jason,
> 
> On Fri, 4 Jun 2021 09:30:37 +0800, Jason Wang <jasowang@...hat.com> wrote:
> 
> > 在 2021/6/4 上午2:19, Jacob Pan 写道:
> > > 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.
> > >  
> > 
> > 
> > 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.
> 
> Yes, in that case we should support both. Give the device driver a chance
> to handle the IOPF if it can.

Huh?

The device driver does not "handle the IOPF" the device driver might
inject the IOPF.

Jason