linux-kernel - Re: [PATCH] Xen/PCI: correct notifier used for device removal

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Message-ID: <56AF578D.6000004@citrix.com>
Date:	Mon, 1 Feb 2016 13:03:09 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Jan Beulich <JBeulich@...e.com>
CC:	xen-devel <xen-devel@...ts.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Xen/PCI: correct notifier used for device removal

On 01/02/16 12:16, Jan Beulich wrote:
>>>> On 01.02.16 at 13:01, <david.vrabel@...rix.com> wrote:
>> On 01/02/16 11:58, Jan Beulich wrote:
>>> Commit 599bad38cf added BUS_NOTIFY_REMOVED_DEVICE in order to allow
>>> avoiding removal of IOMMU mappings before the driver actually got
>>> unbound from the device. Naturally we should be using this too.
>>
>> Because otherwise...?  What happens if we don't make this change?
>>
>> Removing IOMMU mappings for a device when the driver is still bound to
>> the device looks wrong to me. Surely the device is still active and may
>> still be performing DMA at this point?
> 
> Exactly - you answered your own question (as does the commit
> referred to).

I misread, sorry.  I think I will reword this as:

"Commit 599bad38cf added BUS_NOTIFY_REMOVED_DEVICE to defer the removal
of IOMMU mappings until the driver has been unbound from the device
(i.e., until it is guaranteed that there are no outstanding DMA
transactions).

Naturally we should be using this too."

David