linux-kernel - Re: [PATCH v2 09/16] driver core: add iommu device fault reporting data

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Date:   Fri, 6 Oct 2017 00:11:45 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Lan Tianyu <tianyu.lan@...el.com>
Subject: Re: [PATCH v2 09/16] driver core: add iommu device fault reporting
 data

On Thu, Oct 05, 2017 at 04:03:37PM -0700, Jacob Pan wrote:
> DMA faults can be detected by IOMMU at device level. Adding a pointer
> to struct device allows IOMMU subsystem to report relevant faults
> back to the device driver for further handling.
> For direct assigned device (or user space drivers), guest OS holds
> responsibility to handle and respond per device IOMMU fault.
> Therefore we need fault reporting mechanism to propagate faults beyond
> IOMMU subsystem.

We use struct device all over the system, and I don't think we should
bloat it for fringe case IOMMU bits.

Someone really needs to take a step back and figure out how to move
this into a structure that's only allocated for device that actually
can do physical DMA (and/or have an iommu attached)

This is the 3rd iommu field, in addition to 8 dma-specific fields
that we carry around for each struct device.