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Date: Fri, 6 Oct 2017 10:26:03 +0200
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>,
        iommu@lists.linux-foundation.org, LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>, David Woodhouse <dwmw2@infradead.org>,
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        Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
        Lan Tianyu <tianyu.lan@intel.com>
Subject: Re: [PATCH v2 09/16] driver core: add iommu device fault reporting
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Message-ID: <20171006082603.GA3836@kroah.com>
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On Fri, Oct 06, 2017 at 12:11:45AM -0700, Christoph Hellwig wrote:
> 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.

Ick, 8?  Yeah, it's getting big...  How about just a single pointer for
iommu and dma-specific stuff that you all can hang crap like this off
of if needed?

thanks,

greg k-h