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

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Date:   Mon, 21 Mar 2022 09:43:46 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        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

On Mon, Mar 21, 2022 at 11:42:16AM +0000, Jean-Philippe Brucker wrote:

> 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. 

SVA faults should never be reported to drivers??

> 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.

I'm not sure I understand this - we can't match DMAs to executing
CPUs. On fault we fail the DMA and let the process keep running or
SIGSEGV the whole thread group.

Jason