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

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Message-Id: <56AF66E302000078000CCF90@prv-mh.provo.novell.com>
Date:	Mon, 01 Feb 2016 06:08:35 -0700
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"David Vrabel" <david.vrabel@...rix.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 at 14:03, <david.vrabel@...rix.com> wrote:
> 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).

If you want this, then I think you should add "... or IRQs".

Thanks, Jan