linux-kernel - Re: [PATCH 2/2] iommu/vt-d: Only remove domain when device is removed

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Date:	Thu, 6 Nov 2014 13:54:05 +0100
From:	Joerg Roedel <jroedel@...e.de>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	Joerg Roedel <joro@...tes.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Myron Stowe <mstowe@...hat.com>
Subject: Re: [PATCH 2/2] iommu/vt-d: Only remove domain when device is removed

Hi Alex,

On Tue, Nov 04, 2014 at 09:12:17AM -0700, Alex Williamson wrote:
> I haven't tested it, but I'm concerned whether this has introduced a
> domain leak.  If we think about the case of unbinding a device from a
> host driver and attaching it to a domain through the IOMMU API, I think
> we used to count on this path to call domain_exit(), which made the
> domain_context_mapped() in intel_iommu_attach_device() "unlikely".  With
> this change, isn't the test in intel_iommu_attach_device() now neither
> likely nor unlikely and we're only removing the dev_info from the domain
> and not destroying the domain itself?  Thanks,

As I see it, there is no leak. The DMA-API domains are kept in the
device_domain_list and re-used when the device driver re-attaches. But
your are right that the unlikely in intel_iommu_attach_device() isn't
true anymore. We could probably remove it.


	Joerg

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