linux-kernel - Re: [PATCH RFC 10/11] iommu: Make IOPF handling framework generic

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Date:   Mon, 21 Mar 2022 11:42:16 +0000
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 10/11] iommu: Make IOPF handling framework generic

Hi Kevin,

On Mon, Mar 21, 2022 at 08:09:36AM +0000, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@...ux.intel.com>
> > Sent: Sunday, March 20, 2022 2:40 PM
> > 
> > The existing IOPF handling framework only handles the I/O page faults for
> > SVA. Ginven that we are able to link iommu domain with each I/O page fault,
> > we can now make the I/O page fault handling framework more general for
> > more types of page faults.
> 
> "make ... generic" in subject line is kind of confusing. Reading this patch I
> think you really meant changing from per-device fault handling to per-domain
> fault handling. This is more accurate in concept since the fault is caused by
> the domain page table. 😊

I tend to disagree with that last part. The fault is caused by a specific
device accessing shared page tables. We should keep that device
information throughout the fault handling, so that we can report it to the
driver when things go wrong. A process can have multiple threads bound to
different devices, they share the same mm so if the driver wanted to
signal a misbehaving thread, similarly to a SEGV on the CPU side, it would
need the device information to precisely report it to userspace.

Thanks,
Jean